hurricanes

Scratch that Cat: Revising the Saffir-Simpson Scale

British adult orange cat and little kittenIn recent years minimum sea level pressure (MSLP) measured in a hurricane’s eye has become “a much better predictor of hurricane damage” than the maximum sustained wind speed (Vmax) upon which the revered Saffir-Simpson hurricane wind scale is based.

New research by seasonal hurricane forecaster Phil Klotzbach et al. finds that MSLP is also more accurately measurable than Vmax, “making it an ideal quantity for evaluating a hurricane’s potential damage.”

Given that the Saffir-Simpson scale was developed to characterize the risk of hurricanes to the public, we propose classifying hurricanes in the future using MSLP as opposed to Vmax. While no scale will ever perfectly account for the totality of storm risk to life and property (e.g., inland flooding), any improvements to better explain and warn the potential hurricane impacts to an increasingly vulnerable coastal and inland population is, in our view, a worthwhile endeavor.

Klotzbach et al. argue that Vmax is “nearly impossible to measure directly” as the maximum wind mentioned in advisories issued by the National Hurricane Center is the highest 1 minute sustained surface wind occurring “in an unobstructed exposure; (i.e., not blocked by buildings or trees),” which is essentially at sea, not over land. Even with today’s technology, the sparsely observed maximum wind speed is often just an estimate–even land observations are limited by anemometer failure at speeds over 50 kt.

In contrast, MSLP is easy to locate at the storm’s center and is routinely measured by the hurricane hunters in every aircraft reconnaissance mission.

Earlier versions of the Saffir-Simpson scale, created in the early 1970s by engineer Herb Saffir and meteorologist and Hurricane Center director Bob Simpson, incorporated MSLP as a proxy for wind, and they also included ranges by category of storm surge height. But these led to public confusion when actual storm surges and low pressure readings didn’t match up with the categorized winds, and they were removed in 2012.

 Vmax …provides less information on the overall storm risk to life and property than does MSLP. MSLP, on the other hand, is a useful metric in that it is strongly correlated with both Vmax and storm size, which is directly related to storm surge as well as a larger wind and rain footprint. The risk to human life is also more directly correlated to MSLP than to Vmax, given the better relationship of MSLP with storm size. MSLP was a more skillful predictor of fatalities caused by CONUS landfalling hurricanes from 1988-2018 than was Vmax. Consequently, we recommend that more emphasis be placed on MSLP when assessing the potential risks from future landfalling hurricanes.

Saffir-Simpson Hurricane Scale with current Vmax criteria, proposed MSLP criteria and original MSLP criteria from Simpson (1974). Also provided in parentheses are the percentage of Atlantic storms from 1979-2018 whose lifetime maximum intensity exceeded the weakest intensity criteria for each category threshold.
Saffir-Simpson Hurricane Scale with current Vmax criteria, proposed MSLP criteria and original MSLP criteria from Simpson (1974). Also provided in parentheses are the percentage of Atlantic storms from 1979-2018 whose lifetime maximum intensity exceeded the weakest intensity criteria for each category threshold.

 

The difference between using MSLP and Vmax when predicting damage potential has become more noticeable in recent years. This is “likely due to larger-sized hurricanes such as Ike (2008) and Sandy (2012) which did much more damage than would be typically associated with hurricanes making landfall at Category 2 and Category 1 intensity, respectively.” Both storms had much larger storm surges than their category rankings suggested, as did Hurricane Katrina, which was Category 3 at landfall based on Vmax, but had a MSLP equivalent to a Category 5. Its storm surge was measured at a record 28 feet and the resulting damage was catastrophic, consistent with a Cat 5 hurricane.

Using MSLP to re-categorize some historic hurricanes at landfall, the study finds the following:

  • Hurricane Katrina (2005) would go from a Cat 3 to Cat 5;
  • Superstorm Sandy, which was post-tropical but considered “just” a Cat 1 when it made landfall in 2012, would rank as a Cat 4.
  • Hurricane Ike (2008) would be elevated from a Cat 2 to a Cat 3.
  • Hurricane Michael (2018) would have been Cat 5 at landfall rather than a high-end Cat 4 stated in advisories.

The new BAMS paper is available as an Early Online Release. It will be adapted for print and published in the February issue.

What If: Hurricane Michael's Extensive Wind Swath Would Devastate Houston, NWS says

“In summary, it’s going to be bad.”
That’s how Jeff Evans with the NWS in Houston/Galveston began Wednesday’s presentation, “What if Hurricane Michael Struck Houston? An Examination of Inland Wind Damage,” at the AMS 100th Annual Meeting in Boston.
He was boots on the ground after Hurricane Michael slammed the panhandle as a Category 5 with 160 mph winds on October 10, 2018, assisting the Tallahassee NWS office with surveying the widespread wind damage that extended well away from the coast. Because Michael was intensifying at landfall as well as accelerating, its extreme winds spread deep inland, across the panhandle and well into southwest and southern Georgia.
The Donalsonville, Georgia, airport northeast of Marianna, Florida, and about 90 miles inland, recorded a wind gust to 115 mph, while Marianna had a gust to 103 mph in Michael. Both as well as Blountstown, Georgia, suffered significant damage to structures as well as trees.

Track and power outage extent map from Hurricane Michael overlaying a map of Houston. What 95% of the Houston Metro area without power would equate to.
Track and power outage extent map from Hurricane Michael overlaying a map of Houston. What 95% of the Houston Metro area without power would equate to.

Evans overlaid maps of Michael’s track, wind swath, and areal power outages on Houston to show the extent of its damage potential. The entire Houston metro area with 7.1 million people would suffer; 6.9 million would lose power. And damage to homes and devastation to the landscape would mimic the widespread destruction he observed in the Florida panhandle and southern Georgia where entire forests were virtually flattened.
Evans said that as an NWS meteorologist responsible for warning the Houston area if such a scenario threatened he would have a lot of trouble following the standard hurricane mantra, “Run from the water, hide from the wind.”
Rice University in the Houston Metro area is about the same distance from the coast as Blountstown, Florida, which was blasted by Hurricane Michael.
Rice University in the Houston Metro area is about the same distance from the coast as Blountstown, Florida, which was blasted by Hurricane Michael.

“Telling people inland to stay put in such extreme wind conditions is not something I would want to do,” he says.
But, he adds, telling them to get out could prove just as deadly in the mass exodus.
“When you start talking about storms, such as Rita, with 130 mph winds or higher, it’s a spontaneous evacuation.” More than 50 people died just from the evacuation of Houston ahead of that storm, he says
It’s been 37 years since a storm brought a significant wind threat to the Houston area. Hurricane Alicia in 1983 was the last. Hurricane Harvey in 2017 was a widespread catastrophic flood event. Hurricane Ike in 2008 was primarily a surge storm.
“The population in and around Houston has doubled during that time,” Evans says. A 2015 American Community Survey showed more than 130,000 people in just Harris county who live in mobile homes, with thousands more in the surrounding counties.
He conducted the research to raise awareness of a “Michael-like” storm and the immense challenges it would represent.

What If: Hurricane Michael’s Extensive Wind Swath Would Devastate Houston, NWS says

“In summary, it’s going to be bad.”

That’s how Jeff Evans with the NWS in Houston/Galveston began Wednesday’s presentation, “What if Hurricane Michael Struck Houston? An Examination of Inland Wind Damage,” at the AMS 100th Annual Meeting in Boston.

He was boots on the ground after Hurricane Michael slammed the panhandle as a Category 5 with 160 mph winds on October 10, 2018, assisting the Tallahassee NWS office with surveying the widespread wind damage that extended well away from the coast. Because Michael was intensifying at landfall as well as accelerating, its extreme winds spread deep inland, across the panhandle and well into southwest and southern Georgia.

The Donalsonville, Georgia, airport northeast of Marianna, Florida, and about 90 miles inland, recorded a wind gust to 115 mph, while Marianna had a gust to 103 mph in Michael. Both as well as Blountstown, Georgia, suffered significant damage to structures as well as trees.

Track and power outage extent map from Hurricane Michael overlaying a map of Houston. What 95% of the Houston Metro area without power would equate to.
Track and power outage extent map from Hurricane Michael overlaying a map of Houston. What 95% of the Houston Metro area without power would equate to.

Evans overlaid maps of Michael’s track, wind swath, and areal power outages on Houston to show the extent of its damage potential. The entire Houston metro area with 7.1 million people would suffer; 6.9 million would lose power. And damage to homes and devastation to the landscape would mimic the widespread destruction he observed in the Florida panhandle and southern Georgia where entire forests were virtually flattened.

Evans said that as an NWS meteorologist responsible for warning the Houston area if such a scenario threatened he would have a lot of trouble following the standard hurricane mantra, “Run from the water, hide from the wind.”

Rice University in the Houston Metro area is about the same distance from the coast as Blountstown, Florida, which was blasted by Hurricane Michael.
Rice University in the Houston Metro area is about the same distance from the coast as Blountstown, Florida, which was blasted by Hurricane Michael.

“Telling people inland to stay put in such extreme wind conditions is not something I would want to do,” he says.

But, he adds, telling them to get out could prove just as deadly in the mass exodus.

“When you start talking about storms, such as Rita, with 130 mph winds or higher, it’s a spontaneous evacuation.” More than 50 people died just from the evacuation of Houston ahead of that storm, he says

It’s been 37 years since a storm brought a significant wind threat to the Houston area. Hurricane Alicia in 1983 was the last. Hurricane Harvey in 2017 was a widespread catastrophic flood event. Hurricane Ike in 2008 was primarily a surge storm.

“The population in and around Houston has doubled during that time,” Evans says. A 2015 American Community Survey showed more than 130,000 people in just Harris county who live in mobile homes, with thousands more in the surrounding counties.

He conducted the research to raise awareness of a “Michael-like” storm and the immense challenges it would represent.

Students Converse with Air Force Hurricane Hunter Flight Meteorologists, Tornado Field Researcher

Saturday’s Student Conference at the AMS 100th Annual Meeting kicking off in Boston featured a series of Conversations with Professionals to gain insight into a variety of career choices, the work these professionals in our field currently do, and how they got where they are today. This year’s series, in which short introductions are followed by a Q and A session with students, included two meteorologists who fly into hurricanes with the Air Force 53rd Weather Reconnaissance Wing and another who helps c0-operate the Doppler on Wheels radar for tornado field research.

Below is a sampling of questions students asked Lt. Col. Ryan Rickert and Maj. Jeremy DeHart with the AF Hurricane Hunters as well as Karen Kosiba of the Center for Severe Weather Research. The answers have been edited for length and clarity.

Q (Hurricane Hunters): Can you tell us a little about your backgrounds in the Air Force?

A: (Lt. Col. Ryan Rickert) “Meteorology degrees, with active duty [13 years], go to a weather tech school to learn how to deal with military weather, and then pretty much start with your track—go to a main [Air Force] hub weather regional center to learn how to do big, broad forecasting, then … to a different place and forecast for an airfield so your supporting aircraft at the field. But there are different paths you can take: Science, modeling, Army support, Air Force support, many different ways that you can go.

A: (Maj. Jeremy DeHart) “Yeah, I agree. A lot of people think Air Force, military, and are like ‘Oh, I want to do research … it’s not really my cup of tea.’ but there are so many different tracks you can take, and you’re not going to get the breadth of experience you will in the Air Force doing the jobs we did while on active duty. I have a masters degree and they sent me to California for two years [while on active duty], and I was a full-time student and was paid full-time to go to school. And they’ll do that for your Ph.D., go teach at the Air Force Academy … so don’t be scared off by [military] operations.

Lt. Col. Ryan Rickert (r) and Major Jeremy DeHart at Saturday's Conversations with Professionals series.
Lt. Col. Ryan Rickert (r) and Major Jeremy DeHart at Saturday’s Conversations with Professionals series.

Q (Hurricane Hunters): How do you adjust when a hurricane is rapidly intensifying?

A: (Maj. Jeremy DeHart) You’re always adjusting, because it’s never what you exactly expected. We maintain a pressure altitude of 10,000 feet flying into and through the eye of a hurricane. By the time you’re in the eye, in the stronger storms you’re down to 8,000 feet. In Hurricane Wilma, which set a low pressure record, they were flying at 5,000 feet because they didn’t expect it to be that strong, and by the time they got [in the eye] it had bottomed out and the plane flying a 5,000-foot pressure … was down to about a thousand feet and had to pull up.”

A: (Lt. Col. Ryan Rickert) “We don’t do that anymore. We now go in higher. … When we’re briefing we’re changing things. And even in the execution of the mission we constantly have to adjust. … Constantly changing our pattern if there’s a really intense area [of convection] that doesn’t look [on radar] like it’s safe to go through.

Q (Hurricane Hunters): What do you do in the off-season?

A: (Maj. Jeremy DeHart) “We go to a lot of airshows.”

A: (Lt. Col. Ryan Rickert) “We give talks at conferences, promote what we do, find out what kinds of new instruments we want to put on our airplane, things like that.”

A: (Maj. Jeremy DeHart) “A lot of people don’t realize we have a winter storm requirement as well. … We’ll fly a synoptic pattern and just pepper a big storm with [dropwindsondes]. We’ll fly higher, like 30,000 feet or so, and just carpetbomb the whole thing with instruments.”

Q (Tornado Research): What made you target research versus academia on your career path?

A: (Karen Kosiba) “Sometimes when you’re deep in academia you don’t think there’s anything outside academia. I was getting ready to graduate and I had done tons of field research but also applied for jobs in academia, in government … and I got many of those jobs. So I picked what I liked. But even if you don’t know what you’re doing you visualize that you’ll try a little of everything. … When I first started working with the Doppler on Wheels I thought I was going to be a technician … but I started to enjoy some different things and it just ended up this way. Just because you get a bachelor’s, a master’s, a Ph.D., an associate degree—whatever you’re getting your degree in—doesn’t mean you can’t do different jobs.”

Karen Kosiba, with the Center for Severe Weather Research, answers students' questions Saturday at the AMS 100th Annual Meeting.
Karen Kosiba, with the Center for Severe Weather Research, answers students’ questions Saturday at the AMS 100th Annual Meeting.

Q (Tornado Research): Can you elaborate a little on graduate school and how you learned how to write grants?

A: (Karen Kosiba) “For those of you in graduate school, or going to graduate school, you usually work with a professor, and they’re trying to get grants, too. My professor said ‘Hey, you want to write a grant proposal?’ and I was like ‘Sure, let’s write a grant proposal.’  And you don’t really know much about how to write them in graduate school. You can just wing it, or you can have a good mentor, like I did. You know, [as an aside] you think your mentor should be someone exactly like you, and even though you can have someone who likes the same stuff as you, it can be advantageous to find a person who can help you meet your career goals. Someone who understands what you want to do and who you want to be.”

Q (Tornado Research): Do you have any advice for recent graduates who are interested in project-based research rather than forecasting? It seems like a lot of people just take the first thing out there, often university helper.

A: (Karen Kosiba) It’s true. But I think there are more opportunities out there than just waking up and taking those first opportunities. In my case not only did I shop for a mentor but also an advisor who could help me out in the field. Big universities often have big field projects, and they don’t always advertise them as well as they should. It can be tricky to get out and get that experience. But places like NCAR have programs getting [their] people out to do field projects. And the University of Wyoming, NSSL, will have projects going in and out. They’re out there and sometimes you have to do a bit of work to find them. Even if one professor doesn’t have anything, they might know someone who just got funded for a project. And once you’re in them take some responsibilities on … and become an active crew member and contributor to the project.

Report: Hurricane Michael Upgraded to Category 5 at Landfall

2018’s devastating Hurricane Michael struck the Florida panhandle at Mexico Beach and Tyndall Air Force Base in October at Category 5 intensity with 160 mph winds, the National Hurricane Center announced Friday. That’s 5 mph higher than Michael’s wind estimate of 155 mph at the time of landfall.

GOES-16 Pseudo-color image or Hurricane Michael at 1730 UTC October 10, 2018. (Courtesy: NOAA NESDIS)
GOES-16 Pseudo-color image or Hurricane Michael at 1730 UTC October 10, 2018. (Image courtesy: NOAA NESDIS)

 
In its post-storm tropical cyclone report, released the same day, NHC stated it culled an abundance of wind data measurements not available in real-time to add the 5 mph to Michael’s wind intensity. The data came from aircraft reconnaissance, ground observations, satellite intensity estimates, surface pressures, and Doppler radar velocities from Eglin Air Force Base and the NWS in Tallahassee. The report goes in-depth with the data, explaining the observations and identifying those that were believable—a 152 knot (175 mph) aircraft wind measurement at 8,000 feet in the southeast eyewall that yields a surface wind of 137 knots (158 mph)—versus those that were suspect—a 152 knot (175 mph) surface wind measured by the stepped frequency microwave radiometer (SFMR) instrument aboard a different aircraft, deemed too high based on experience with such intense winds in hurricanes Irma, Jose, and Maria in 2017.
The upgrade makes Michael only the fourth Category 5 hurricane to hit the United States, joining a small, elite group of monster landfalling storms that include Hurricane Andrew (1992, 165 mph winds), Hurricane Camille (1969, 175 mph winds), and the Labor Day Hurricane (1935, 185 mph winds). Andrew plowed into South Florida, Camille landed on the Mississippi coast, and the Labor Day Hurricane devastated the Florida Keys.
A realty building destroyed by Hurricane Michael's winds on the east of Panama City, Florida.
A realty building destroyed by Hurricane Michael’s winds on the east side of Panama City, Florida.
(Photo courtesy: Chris Cappella [AMS])
 
Hurricane Michael roared ashore on October 10 as the strongest hurricane on record to strike the Florida Panhandle, with a storm surge around 14 feet above ground level, destroying Mexico Beach and much of Tyndall AFB, while tearing apart homes and businesses in Callaway, just inland, as well as in the eastern side of Panama City. Sixteen people died directly from the hurricane due to storm surge flooding and the intense winds, which blew down entire forests in the panhandle and destroyed crops across southern Georgia. Wind damage extended into the Carolinas.
Very few surface observations of the hurricane’s intense winds were made at landfall. The highest gust was 139 mph measured by an anemometer at Tyndall AFB before it failed. Two coastal monitoring program towers measured 129 mph and 125 mph, substantially lower than the upgraded wind speed at landfall. One of the towers was knocked over before the peak winds struck, and the other was outside the hurricane’s core. NHC notes that the sites “were likely not optimally located to sample the maximum winds, which is typical during landfalling hurricanes.”

Eight Decades: Mapping New England Catastrophe

Eighty years ago today (September 21st), the Great New England Hurricane of 1938 ripped across New York’s Long Island and slammed into the Northeast, killing more than 600 people and clawing its way across New England and the record books. Every hurricane to strike the region since is compared to this behemoth, and none has come close to its devastating intensity.

U.S. Weather Bureau surface weather map for 7:30 a.m. ET Wednesday, September 21, 1938.
U.S. Weather Bureau surface weather map for 7:30 a.m. ET Wednesday, September 21, 1938.

 
Ferocious winds gusting beyond category 5 intensity and an enormous storm surge that wiped out coastal Long Island and flooded into Rhode Island and Connecticut were its hallmarks. Copious rains also brought by the hurricane fell on soils swamped by heavy rain just days before the storm, leading to widespread flooding and thousands of landslides. Eight decades. And its imprint is still being realized.
Recently, new precipitation data on the storm and a precursor heavy rain event—now understood to be ubiquitous before New England hurricanes—were found. This precipitation map (right) newly appears in the 2nd edition of Taken by Storm 1938: a comprehensive social and meteorological history of the Great New England Hurricane, by Lourdes B. Avilés, professor of meteorology at Plymouth State University.
Precipitation observed during the Great New England Hurricane and its predecessor rain event. (U.S. Geological Survey)
Precipitation observed during the Great New England Hurricane and its predecessor rain event.
(U.S. Geological Survey)

 
The map was created by a grad student Avilés was advising—Lauren Carter—who painstakingly digitized thousands of observations from more than 700 daily weather stations Avilés had unearthed, spanning the 6-day event. This unique updated rainfall map is just one of many new and interesting finds detailed in the new edition of her book, which is now available in the AMS Bookstore. The book’s website houses supplemental information, including more color rainfall maps, detailed reports, and photos.

How Hurricane Florence Could Turn Weird and Deadly

Hurricane Florence is forecast to slow to a crawl as it nears landfall in the next 24 hours. As a result, some unusual and unimaginable things could happen. People in the Carolinas need to take this hurricane seriously. Even veterans of past landfalls there may be in for a surprise.
For starters, slow-moving hurricanes often deliver flood disasters. Think last year’s Hurricane Harvey with its 50- to 60-inch rains. The National Weather Service is predicting widespread rainfall in parts of the Carolinas of 10-20 inches. And some areas could be inundated with 30-50 inches as rainbands spiral ashore and hit spots repeatedly, as they did for days in Texas during Harvey.

NWS prediction of rainfall from Hurricane Florence over the next week.
NWS prediction of rainfall from Hurricane Florence over the next week.

 
Then there’s the storm surge. It may be unprecedented. Sure the Carolinas have endured the likes of Hurricanes Hugo in 1989, Fran in 1996, and Hazel in 1954. All brought storm surges topping 15 feet. But all were also moving quickly. A slowing hurricane like Florence could pile up a lot of water.
If it stalls offshore, says storm surge expert Dr. Hal Needham in a Wednesday blog post, “this will serve to dramatically increase the storm surge magnitude and geographic extent of coastal flooding.”
Already the National Hurricane Center expects some portions of the North Carolina coast to realize surge levels of 9-13 feet. A stalling storm piling even more water onto even more of the coast?
Needham points out an “unthinkable,” seeing that forecast models show “Florence making landfall on Thursday evening…and Florence still making landfall on Friday evening. A slow-moving hurricane tracking near a coastline is bad news indeed, as it enables the storm to inflict destructive storm surge along an extended area.”
What’s worse is that the collapsing steering currents may not just delay landfall but also could lead to the hurricane drifting southwest with its core paralleling the South Carolina coast. Initial offshore winds that are increasing as the center moves closer to any point on the coast would drive water ashore in ways unseen in other landfalling hurricanes. Intracoastal waterways could flood barrier islands on their landward sides, and previous precautions for flooding may not be sufficient.
A recent example is 2017’s Hurricane Irma flooding coastal Jacksonville, Florida. When landfalling storms approach Jacksonville from the Atlantic Ocean, winds initially blow from north-to-south. But Irma’s huge wind field instead whipped up a coastal surge from the south, swamping places unaccustomed to surge.
But Florence’s surges may be more than a directional oddity. The hurricane’s offshore winds will initially push tremendous amounts of water away from the coast, much like offshore winds emptied Tampa Bay, Florida as Irma approached. As Florence’s center then passes, Needham explains, “powerful winds in the hurricane’s eyewall, the most intense part of the storm, would immediately shift from offshore to onshore, producing a destructive storm surge in the matter of minutes.” Such sudden, extreme changes are likely to catch residents off guard.
It happened recently in The Philippines. Supertyphoon Hainan’s surge came ashore like a tsunami, Needham says, as the wind shifted direction. He notes that 2013’s Hainan was one of the most intense tropical cyclones to make landfall in recorded history, and he doesn’t expect the surge from Hurricane Florence to move as rapidly.
Still, such a sudden reversal of high winds from a hurricane moving unusually from north to south off the South Carolina coast would push storm surge quickly ashore, devastating the shoreline.
Expect the unexpected with Hurricane Florence. If local authorities tell you to leave, get out.

1871 Hawaii Hurricane Strike Shows Lane's Imminent Danger Isn't Unprecedented

Powerful Hurricane Lane is forecast to skirt if not directly hit Hawaii as a slowly weakening major hurricane today and Friday. Its track is unusual: most Central Pacific hurricanes either steer well south of the tropical paradise or fall apart upon approaching the islands. But a recent paper in the Bulletin of the AMS reveals that such intense tropical cyclones menace Hawaii more frequently than previously thought.
Hurricane Lane as of Thursday morning local time was packing sustained winds of 130 mph with gusts topping 160. Its expected track (below) is northward toward the middle islands today and early tomorrow, followed by a sharp left turn later Friday. When that left hook occurs will determine the severity of the impacts on Maui as well as Oahu, home to Hawaii’s capital and largest city, Honolulu. Although Lane is expected to slowly weaken due to increasing wind shear aloft, it appears that the Big Island of Hawaii, Maui, Molokai, and Oahu will be raked at a minimum by tropical storm winds gusting 55-70 mph, pounding surf, and heavy, potentially flooding rain. Hurricane conditions on these islands also are possible.

Three-day track forecast for Hurricane Lane's approach to Hawaii.
Three-day track forecast for Hurricane Lane’s approach to Hawaii (Central Pacific Hurricane Center).

The last major hurricane to affect the islands with more than swells and heavy surf was Hurricane Iniki in 1992. It was passing well south of the islands when an approaching upper-air trough brought in steering flow out of the south, and Iniki made a right turn toward the western islands while intensifying into a strong Category 4 hurricane. It slammed directly into the garden island of Kauai with average winds of 145 mph and extreme gusts that damaged or destroyed more than 90 percent of the homes and buildings on the island. Iniki obliterated  Kauai’s lush landscape, seen in its full splendor in such movies as Jurassic Park, which was filming there as the storm bore down.
The only other known direct hit on Hawaii was by 1959’s Hurricane Dot, which was a minimal Category 1 storm–the winds barely reaching threshold hurricane intensity of 74 mph when its center crossed Kauai. Without any prior record of major hurricane landfall, Iniki was not just rare, it was considered unprecedented.
Until now.
More than a century before Iniki, a major hurricane crashed into the Big Island, its intense right-front quadrant passing directly over neighboring Maui, causing widespread devastation on both islands. Its discovery is outlined in Hurricane with a History: Hawaiian Newspapers Illuminate an 1871 Storm, which details the narrative thanks to an explosion of literacy on the islands in the mid 19th century, which led to hundreds of local language newspapers that published eyewitness accounts of the storm.
Map showing the reconstructed track of the Hawaii hurricane across the eastern islands of Hawaii and Maui on 9 Aug 1871. Labeled red circles indicate the approximate time and location of the core of the storm. Green shading shows terrain altitude every 2,000 ft (610 m).
Map showing the reconstructed track of the Hawaii hurricane across the eastern islands of Hawaii and Maui on 9 Aug 1871. Labeled red circles indicate the approximate time and location of the core of the storm. Green shading shows terrain altitude every 2,000 ft (610 m).

The new historical research, published in the January 2018 BAMS, found unequivocal evidence of an intense hurricane that struck August 9, 1871, causing widespread destruction from Hilo on the eastern side of the Big Island to Lahaina on Maui’s west side. A Hawaiian-language newspaper archive of more than 125,000 pages digitized and now made publicly available along with translated articles contained account after account of incredible damage that led the paper’s authors to surmise that at least a Category 3 if not a Category 4 hurricane hit that day.
The paper’s analysis is put forth as “the first to rely on the written record from an indigenous people” of storms, droughts, volcanic eruptions, and other extreme natural events. Accounts published in Hawaiian newspapers create a living history of the 1871 hurricane’s devastation, as recounted in the paper:
“On the island of Hawaii, the hurricane first struck the Hāmākua coast and Waipi‘o valley. The following is from a reader’s letter from Waipi‘o dated 16 August 1871:”

At about 7 or 8 AM it commenced to blow and it lasted for about an hour and a half, blowing right up the valley. There were 28 houses blown clean away and many more partially destroyed. There is hardly a  tree  or  bush  of  any  kind  standing  in  the  valley (Pacific Commercial Advertiser on 19 August 1871).

“An eyewitness from Kohala on Hawaii Island wrote the following:”

The greatest fury was say from 9 to 9:30 or 9:45, torrents of rain came with it. The district is swept as with the besom of destruction. About 150 houses were blown down. A mango tree was snapped as a pipe stem, just above the surface of the ground. Old solid Kukui trees, which had stood the storms of a score of years were torn up and pitched about like chaff. Dr. Wright’s mill and sugarhouse, the trash and manager’s residence, were all strewn over the ground (Ke Au Okoa on 24 August 1871).

“On Maui, newspaper reports document that Hāna, Wailuku, and Lahaina were particularly hard-hit. A writer in Hāna described the storm:”

Then the strong, fierce presence of the wind and rain finally came, and the simple Hawaiian houses and the wooden houses of the residents here in Hāna were knocked down. They were overturned and moved by the strength of that which hears not when spoken to (Ka Nupepa Kuokoa on 26 August 1871).

“In Wailuku the bridge was destroyed:”

… the bridge turned like a ship overturned by the carpenters, and it was like a mast-less ship on an unlucky sail.” (Ka Nupepa Kuokoa on 19 August 1871).

“From Lahaina came the following report:”

It commenced lightly on Tuesday night, with a gentle breeze, up to daylight on Wednesday, when the rain began to pour in proportion, from the westward, veering round to all points, becoming a perfect hurricane, thrashing and crashing among the trees and shrubbery, while the streams and fishponds overflowed and the land was flooded (Pacific Commercial Advertiser on 19 August 1871).

The BAMS paper concludes that the 1871 hurricane was “a compact storm, similar to Iniki.” Honolulu escaped damaging winds or rain despite such a close encounter.
Because such historical records have been unnoticed for so long, the paper notes “a number of myths have arisen such as ‘the volcanoes protect us,’ ‘only Kauai gets hit,’ or ‘there is no Hawaiian word for hurricane.’”
Today’s powerful Hurricane Lane and the newfound historical records go a long way to dispelling these misconceptions about the threat of hurricanes in the Hawaiian Islands.
 

Future Hurricanes a Bit Stronger and Slower, but Much Wetter in a Warmer Climate

It’s been more than 8 months. Since Maria. Irma before. And Harvey before that. For many who endured them, it was yesterday. And here we are at the start of another hurricane season.
2018-NOAA-hurricane-numbersWhat can we expect? It is nearly indisputable that there will be hurricanes. NOAA’s forecast issued last week calls for 5-9 of them this year. Will they strike land? Science can’t yet say whether any hurricanes and tropical storms will or won’t later this season. It depends on atmospheric steering currents in the Atlantic basin and how they set up this year, particularly during the heart of the six-month season—from August through October.
But new research is looking beyond this season, beyond many seasons, and is discovering a different type of hurricane season less than 80 years from now, as Earth’s climate warms.
The new study published in the Journal of Climate finds that near-future hurricanes will be wetter and stronger, and they likely will move slower than before, increasing the risk of serious landfall flooding.
Scientists analyzed more than 20 recent hurricanes to determine how they might change near the end of this century, assuming an increase in global temperatures. One such hurricane—Ike from 2010, which inundated coastal Texas, killing more than 100 people and obliterating the popular Bolivar Peninsula barrier island north of Galveston, would have 13 percent stronger winds, move 17 percent slower, and be 34 percent wetter in a warmer world.
Others might move faster and be slightly weaker. But none of the storms reanimated in the future became drier.
“Our research suggests that future hurricanes could drop significantly more rain,” says NCAR scientist Ethan Gutmann, who led the study. Hurricane Harvey unloaded three to four feet of rain in a wide swath from Victoria, Texas, across the Houston area and into Port Arthur in extreme eastern Texas, breaking records and causing devastating flooding, and demonstrating “just how dangerous that can be,” Gutmann says.
That danger is being magnified as coastal populations continue to exponentially grow. “The potential influence of climate change on hurricanes has significant implications for public safety and the economy,” NCAR stated in a release about the new research. The study showed that “the number of strong hurricanes, as a percent of total hurricanes each year, may increase,” Ed Bensman, an NSF program director in the Division of Atmospheric and Geospace Sciences, says. “With increased development along coastlines, that has important implications for future storm damage.”
NSF supported the study, which viewed future hurricanes for the first time collectively at high resolution. Past studies looking at how hurricanes may change in a warmer climate have relied on climate model projections that are determined on a global scale and with temporal resolution of decades to centuries. Their resolution is too low to “see” future hurricanes. Weather models, on the other hand, can see them, but they aren’t used to see long-term because of the high costs of running them.
With the new research, scientists made use of an enormous NCAR dataset and ran the Weather Research and Forecasting (WRF) model at a high resolution (4 kilometers, or about 2.5 miles) focused on the lower 48 United States for two 13-year periods. The first determined the weather as it happened between 2000 and 2013 and the second simulated the same weather but with a climate 5° C (9° F) hotter and subsequently wetter that was warmed near the end of this century by unabated greenhouse gas emissions.
Comparing 22 historic Atlantic hurricanes to the same number of future hurricanes with very similar tracks found a collective 6 percent increase in top wind speeds, but a 24 percent increase in average rain rates. The future storms moved 9 percent slower than in the past.
Individually, each hurricane was unique, some changing one way and others differently. All were rainier. And while other studies have suggested that increases in atmospheric stability and wind shear may lower the total number of annual hurricanes and tropical storms, “from this study we get an idea of what we can expect from the storms that do form,” Gutmann says, and they are likely to be more intense.
2018-Hurricane-namesThere isn’t a way to tell yet what this year’s hurricanes will be like. But it’s another year into our warming world, and this is yet another study pointing to ominous changes with hurricanes in our future.

Small-scale Vortices Enhanced Winds and Damage in Hurricane Harvey

Severe but highly variable wind damage to homes & infrastructure is a hallmark of intense tropical cyclones. Until recently there was only speculation that such damage, which appears in short swaths, was the work of tornadoes. Now, there’s first-ever proof that tornadoes and other small-scale phenomena did indeed enhance the winds and damage in Hurricane Harvey last August.

Fine-scale Doppler On Wheels (DOW) radar imagery collected from inside the eyewall of Hurricane Harvey (Left: radar reflectivity, Right: Doppler velocity). The ring of convection comprising the eyewall is highly perturbed by four MVs (labeled A-D). From inside the eye, the wind perturbations caused by the MVs are especially visible. DOW location is yellow dot. Black rectangle is zoomed-in area shown in separate figure illustrating tornado-scale vortices.
Fine-scale DOW radar imagery from inside the eyewall of Hurricane Harvey (Left: radar reflectivity, Right: Doppler velocity). The ring of convection comprising the eyewall is highly perturbed by four MVs (labeled A-D). From inside the eye, the wind perturbations caused by the MVs are especially visible. DOW location is the yellow dot. Black rectangle is zoomed-in area shown in figure below illustrating tornado-scale vortices.

 
Doppler of Wheels (DOW) radar in the eye of Harvey revealed mesovortices (MVs) rotating swiftly around the inner eyewall, and embedded in them and documented for the first time were small tornado-scale-vortices (TSVs) less than a half-mile wide spinning within the larger wind field of the hurricane. The discovery was reported in March in a paper published in Monthly Weather Review.
The rotation of the TSVs is weaker than typical supercell tornadoes, but because these circulating winds are embedded in an already extreme eyewall, they ramp up the wind speed and create greatly enhanced damage potential, says the study’s lead author Joshua Wurman of the Center for Severe Weather Research. In Harvey, major hurricane winds of about 120 mph ramped up to 130-140 mph or more and resulted in streaks of severe damage not evident elsewhere from the eyewall winds.
“Wind gusts at the DOW site were measured up to 145 mph, likely caused by a TSV, and 30% of the vehicles parked near the DOW were lofted,” Wurman wrote in a summary of the paper to appear in a forthcoming issue of the Bulletin of the AMS. A Jeep and two SUVs were picked up by the wind and landed atop debris from the destroyed building in which they were housed. He said the swaths of intense damage corresponded to the tracks of the eyewall TSVs.
Doppler velocity data reveals single and paired TSVs (demarked schematically with black circles) translating rapidly southward in Harvey’s northwestern eyewall embedded in strong northerly flow (black arrow). These TSVs, moving southward at up to 120 mph, were associated with very intense winds measured up to 145 mph, lofted vehicles, and swaths of the most intense building damage.

Doppler velocity data reveals single and paired TSVs (black circles) translating southward in Harvey’s northwestern eyewall embedded in strong northerly flow (black arrow). These TSVs, moving southward at up to 120 mph, were associated with very intense winds measured up to 145 mph, lofted vehicles, and swaths of the most intense building damage.

 
Wurman and co-author Karen Kosiba, also with CSWR, will present their research findings from Hurricane Harvey as well as newly identified evidence of at least one Harvey-like TSV in Hurricane Irma over Florida at the 33rd AMS Conference on Hurricanes and Tropical Meteorology next week in Ponte Vedra Beach, Florida. The conference will feature a number of other presentations on the devastating hurricanes of 2017, in multiple sessions (Session 1, Session 2, Session 3, Session 4).
Intense wind gusts, likely caused by tornado-scale vortices in Harvey’s eyewall, lofted SUV-type vehicles (red arrows; green arrows point to unlofted vehicles). Wind gusts as intense as 145 mph were measured by a DOW-mounted anemometer 350 m downstream from these lofted vehicles.
Intense wind gusts, likely caused by TSVs in Harvey’s eyewall, lofted SUV-type vehicles (red arrows; green arrows point to unlofted vehicles). Wind gusts as intense as 145 mph were measured by a DOW-mounted anemometer 350 m downstream from these lofted vehicles.

 
Wurman notes that it’s unclear whether the new wind whirls are more numerous in intense or rapidly strengthening hurricanes. But adds that the enhanced damage was palpable, and with an increase in powerful hurricanes possible due to rising global air and ocean temperatures, it’s important to learn more about them, he says.
“Potential climate change may result in more frequent intense and/or rapidly intensifying hurricanes, thus understanding and forecasting the causes of hurricane wind damage is a high priority.”