tropical cyclones

Improving Tropical Cyclone Forecasts

Tropical cyclones are usually associated with bad news, but a long-term study about these storms now posted online for publication in BAMS has some good news–about the forecasts, at least. The authors, a Japanese group lead by Munehiko Yamaguchi, studied operational global numerical model forecasts of tropical cyclones since 1991.
Their finding: the model forecasts of storm positions have improved in the last 25 years. In the Western North Pacific, for example, lead time is two-and-a-half days better. Across the globe, errors in 1 – 5 day forecasts dipped by 6 to 14.5 km, depending on the basin.
Here are the improvements for the globe as a whole. Each line is a different modeling center:
CycloneForecastsGlobal
While position forecasts with a single model are getting better (not so much with intensity forecasts), it seems natural that the use of a consensus of the best models could improve results even more. But Yamaguchi et al. say that’s not true in every ocean basin. The result is not enhanced in the Southern Indian Ocean, for example. The authors explain:

This would be due to the fact that the difference of the position errors of the best three NWP centers is large rather than comparable with each other and thus limits the impact of a consensus approach.

The authors point towards ways to improve tropical cyclone track forecasts, because not all storms behave the same:

while the mean error is decreasing, there still exist many cases in which the errors are extremely large. In other words, there is still a potential to further reduce the annual average TC position errors by reducing the number of such large-error cases.

For example, take 5-day track forecasts for Hurricane Joaquin in 2015. Hard to find a useful consensus here (the black line is the eventual track):
JoaquinForecast
Yamaguchi et al. note that these are types of situations that warrant more study, and might yield the next leaps in improvement. They note that the range of forecast possibilities now mapped as a “cone of uncertainty” could be improved by adapting to specific situations:

For straight tracks, 90% of the cyclonic disturbances would lie within the cone, but only 39% of the recurving or looping tracks would be within the cone. Thus a situation-dependent track forecast confidence display would be clearly more appropriate.

Check out the article for more of Yamaguchi et al.’s global perspective on how tropical cyclone forecasts have improved, and could continue to improve.

Survivors Meet the Storm

As  Typhoon Hagupit (Ruby) headed their way this weekend, Filipinos began to show they were a people far too experienced in the ways of typhoons.
Anxiety mixed with prudence. 500,000 people evacuated to safer quarters. Many residents of Tacloban–the city hardest hit by last year’s disastrous Typhoon Haiyan—took shelter in the local stadium. Others stocked up with food and other supplies. The city’s deputy mayor told the BBC, “It’s stirring up a lot of emotions in our hearts and bringing back so many painful memories.”
Those who study severe weather warnings are increasingly noticing this phenomenon: whether by fear or familiarity, people with prior experience have a peculiarly complex reaction to impending severe weather.
For example, a succession of well predicted tornadoes hit central Oklahoma within a short span in May 2013. During the third outbreak of that period, public reaction went awry. Before meteorologists could warn of the dangers of fleeing by car, residents hit the roads and caused potentially catastrophic traffic jams. The spontaneous evacuation, unlike any seen previously for a tornado, exposed the public to great risks.
In a paper to be presented at the AMS Annual Meeting next month at the Phoenix Convention Center (Wednesday, 7 January, 11:15 a.m., Room 226AB), Julia Ross and colleagues will analyze the effects of experience on the public’s “freak out” response to these tornadoes.
Quoting a recent paper by Silver and Andrey in the AMS journal, Weather, Climate, and Society, Ross et al. note that direct experience with hazards amplifies risk perception.  But their survey results show both reasoned and fear-driven reactions to the warnings—and possibly some regionally specific preferences as well.
(In the presentation to follow Ross et al. at the Annual Meeting, Lisa Dilling and colleagues analyze the opposite of a wary, seasoned public. They report on the effect of surprise in the Boulder, Colorado, floods last year.)
If anyone knows typhoons, it’s the people of the Philippines. Supertyphoon Haiyan, which killed 7,000 a year ago, was but one of six different tropical cyclones that have killed more than 1,000 Filipinos in the past decade.
This time around authorities say they’re aiming for zero casualties. But there’s more than just anxiety to deal with. It takes time to rebuild from a blow like Haiyan. A Haiyan survivor in Tacloban told the Associated Press, “I’m scared. “I’m praying to God not to let another disaster strike us again. We haven’t recovered from the first.”
 

Time to Heed the Hurricane Season Forecast?

With this year’s Atlantic hurricane season getting underway, seasonal forecasts are collectively calling for a quieter-than-usual year in the Atlantic basin, which includes the Caribbean Sea and Gulf of Mexico. With busts in these forecasts as recent as last year, however, is this actually reassuring news?
Mark Powell, a NOAA hurricane researcher who is now working with Florida State University’s Center for Ocean-Atmospheric Prediction Studies, was quoted in a recent Palm Beach Daily News article saying such forecasts, which typically are made before the start of the six-month season, “just don’t have any skill this early.”
They practically don’t. The major players of Atlantic hurricane season forecasts—NOAA, Colorado State University (CSU), and the private British forecasting firm Tropical Storm Risk (TSR)—stipulate that there is only a small increase in skill with pre-season forecasts (i.e., how much better such forecasts are) compared to climatology in foretelling the number of named storms that will form in the Atlantic basin from June 1 to November 30. Supporting this, a talk by Eric Blake of the National Hurricane Center presented at the 29th AMS Conference on Hurricanes and Tropical Meteorology stated that NOAA’s May forecasts for anticipated numbers of storms and hurricanes are only slightly better than what climatology showed had occurred in the previous five seasons. Forecast skill does increase as the season nears its peak months: August, September, and October, which is when 70 percent of tropical storms and hurricanes form.
But even these “better” mid-season forecasts can be wrong. In 2013, early predictions for an active season remained high as September neared, yet the actual number of named storms (13) and especially hurricanes (just 2) fell short of most forecasts, which had been collectively predicting a blockbuster season with at least seven hurricanes and three major hurricanes. The long-term average number of named storms and hurricanes is 12 and 6, respectively. There wasn’t a single major hurricane sporting winds greater than 110 mph last year, when climatology said there should have been at least three. In a blog post at the end of last year’s season, Jeff Masters of WeatherUnderground.com detailed the reason the forecasts failed: the large-scale atmospheric circulation, which can’t be predicted more than a week or two out and isn’t part of seasonal forecasts, was not conducive to tropical cyclone formation.
In 2012, however, it was, and the opposite occurred. The number of named storms peaked at 19—not only well above average but also the third highest number of storms on record in a single season. Ten of these went on to become hurricanes, exceeding most seasonal forecasts including NOAA’s, which had called for an average Atlantic hurricane season prior to its start. CSU had projected in June of that year a relatively quiet hurricane season with 13 named storms and only 5 hurricanes. With twice that many hurricanes forming, the season blew the forecast out of the water, making it CSU’s worst bust in decades of predictions. Until 2013.
This year, however, hurricane season forecasters feel the chance of the development of El Niño by the fall is much higher than it was in 2012—70 percent this summer increasing to 80 percent by fall, according to NOAA’s 9 June El Niño status statement—which lends significant weight to the lower hurricane predictions.
Historically, El Niño stifles Atlantic hurricanes. The enormous slug of warmer-than-normal sea surface temperatures along the Eastern Pacific equator, which defines El Niño, imparts a shift in the atmosphere’s circulation that drives unusually strong winds at high altitudes across the tropical Atlantic Ocean during the season. The induced wind shear—a difference in both speed and direction between the surface and aloft—suppresses not only tropical cyclone development but also formation, tearing apart hurricane seedlings before they can organize.
Research in recent years (Journal of Climate: 2009, 2013), however, has shown that a very different effect can result from El Niño’s half-brother – an anomalous warming in the tropical Pacific that pools in the central rather than the eastern part of the ocean basin. When this occurs, as it did in 2004, it can actually amplify the Atlantic hurricane season. That year, four hurricanes—three of them major, including Charley with 150 mph winds—slammed Florida. There were 15 named storms that year.
No forecasters expect a repeat of the devastating 2004 hurricane season. But, already we’ve had a record eight hurricane seasons without landfall of a major hurricane in the United States nor any category hurricane striking Florida. The last one was Wilma in 2005, which hit as a major hurricane.
Whether or not forecasts are accurate this early in the season, the old adage still applies: it only takes one hurricane in your area to create disaster. So be prepared.

The Storm That Started a Drought?

by Robert V. Sobczak, National Park Service, Big Cypress National Preserve.
Reposted from his blog, The South Florida Watershed Journal.
Do all storms end with drought?
I know you’re thinking. I mean the opposite instead:
That “all droughts end with a flood,” right?

Deer Creek
Deer Creek, Maryland at low-water autumn ebb.

A meteorologist in the snow-bound climes of the Red River Basin introduced me to the latter saying. To what degree it holds any statistical truth I cannot say. My initial gut reaction was that an observational bias was in play, plus some seasonal slight of hand. But no matter how much I tried to deny it, the saying kept sneaking up on me wherever I roamed.
Take Tropical Depression Nicole for example. It threatened to make our already high-water rendition of the Big Cypress Swamp all the more wetter but by the flap of the wings of the butterfly bypassed to the east and then onward north to the Atlantic Coast where it drenched those watersheds instead.
Now here’s the catch:
Those watersheds were at the end of their seasonal drought, better known as the summer recession, transforming currents from trickles into torrents overnight.
So yes, chalk one on the board for that old reliable saying!

Case in point is Maryland’s Deer Creek, as measured at Rocks State Park (or just “Rocks” as us Harford Countians call it). Thanks to Nicole it now has a chance to top 40 Empire State Buildings (ESBs) worth of water flow for the year. That would make it an above average year, but not a “chart topper,” a term I reserve for the biggest of big flow years which pass 60 or more ESBs worth of water. That’s happened just four times in the modern era (aka my lifetime), the most recent of which (2003) which was, as predicted by that old reliable saying, preceded by the drought of record in 2002 when less than 20 ESBs worth of water flowed through Maryland’s famed Rocks State Park for the year.
Ha, there it is again! So, cherry picking not withstanding, I guess that means that, yes, all drought do seem to end with floods.

Does the same saying apply to the Florida swamps?
Seasonally it happens each year with our winter dry season. By spring the swamps are nearly 100 percent water free and crunchy, just a single lightning strike away from an uncontrollable blaze. But along with the lighting are the thunder that beckon the wet season’s arrival … and the floods that will soon be to follow.
Which brings me back to Nicole:
Instead of flushing flood waters even higher into the swamp it paradoxically reversed the tables by ushering in a week’s worth of dry air in its wake instead.
Meteorologists are calling it an early start to the dry season.

Loop Road near Gator Hook Strand at the wet-season peak.

Or in other words…
Call it the storm that started the drought!

A Slow Start, but Gaining Fast

Tropical Storm Lisa became the 12th named storm in the Atlantic Basin this week in what has suddenly become the active 2010 hurricane season that forecasters months ago had predicted. Nine of those twelve storms formed since August 21, with five of them becoming hurricanes. Before that, only one of the first three named storms (Alex) even reached hurricane strength. By contrast, 2005 (9 out of 28) and 2008 (6 out of 16)  both had numerous storms form before August 20. Why the delay this year? According to a story in Newscientist.com, a mass of hot, dry air over the oceans stunted the formation of tropical storms. Scientists traced this dry air to a massive ridge of high pressure that sat for months over Europe and Asia, causing an intense heatwave in Russia and severe monsoon rains in Pakistan this summer that killed thousands of people. But just as mid-August arrived, when the typical height of Atlantic hurricane activity is imminent, things changed. As the Weather Underground’s Jeff Masters wrote in his blog on August 17:

Vertical instability, which was unusually low since late July, has now returned to near normal levels over the tropical Atlantic, though it remains quite low over the rest of the North Atlantic. Instability is measured as the difference in temperature between the surface and the top of the troposphere (the highest altitude that thunderstorm tops can penetrate to). If the surface is very warm and the top of the troposphere is cold, an unstable atmosphere results, which helps to enhance thunderstorm updrafts and promotes hurricane development. Since SSTs in the Atlantic were at record highs and upper tropospheric temperatures were several degrees cooler than average in July, enhancing instability, something else must have been going on to reduce instability. Dry air can act to reduce instability, and it appears that an unusually dry atmosphere, due to large-scale sinking over the Atlantic, was responsible for the lack of instability.

Not until the heat wave broke near the end of August did the tropical storms really begin to form in earnest, with four storms (Danielle, Earl, Fiona, and Gaston) arising just between August 21 and September 1. And spurred by those record-high SSTs mentioned by Masters, the 2010 season has not only produced 12 named storms and 6 hurricanes, but 5 major hurricanes–four of them Category 4–making that slow start seem like a distant memory. To put this season in historical perspective, there have been yearly averages of 14 named storms, 8 hurricanes, and 4 major hurricanes since the current active Atlantic hurricane period began in 1995. This season is just one major hurricane away from moving into a 7-way tie for 3rd-most major hurricanes in a season, topped only by the 7 major hurricanes in 1961 and 2005 and 8 in 1950 (lists of most active seasons in various categories can be found here).

This photo, taken from the International Space Station, shows the eye of Category-4 Hurricane Igor at 10:56 Atlantic Daylight Time on September 14, 2010, as it advanced over the Atlantic Ocean. (Photo credit: NASA Earth Observatory.)

Inside Earl

NASA’s GRIP mission (Genesis and Rapid Intensification Processes) is sending aircraft into Hurricane Earl, coming up with some wonderful imagery from almost 20,000 meters above the ocean surface. Here’s how the eye looked from the Global Hawk unmanned aircraft at 9:05 a.m. Eastern, Thursday:

For more on GRIP, Earl, the Global Hawk, and the importance of having drones that can fly up to 26 hours in a single mission, this video interview with Jeff Halverson gives some answers with nice imagery:

Remembering Katrina and New Orleans

by William Hooke, AMS Policy Program Director, from the AMS project, Living on the Real World

“…we can not dedicate, we can not consecrate – we can not hallow – this ground. The brave men, living and dead, who struggled here, have consecrated it far above our poor power to add or detract.”– Abraham Lincoln, Gettysburg address

The last few posts, as we’ve started to think about disasters, we’ve asked, what’s it worth to see a disaster coming? Katrina shows vividly that it’s worth relatively little if we can’t or won’t act. People had been vocal about the growth of vulnerability in New Orleans for decades, even as the vulnerability and risks ratcheted up. The warnings didn’t seem to be enough.
Some salient features of this landscape? Well, for one, the 2002 series of articles by Mark Schleifstein and John McQuaid in the New Orleans Times-Picayune, “Washing Away: how south Louisiana is growing more vulnerable to a catastrophic hurricane.” For another, the 2004 article by Shirley Laska in The Natural Hazards Observer, “What if Hurricane Ivan had not missed New Orleans,” and her June 2005 talk as part of an AMS environmental science seminar on Capitol Hill, in the Senate Hart Office Building, on the topic of “New Orleans, hurricanes, and climate change: a question of resiliency.” That afternoon, one hundred policymakers were in the room, including U.S. Senator Mary Landrieu (D-LA, who to her credit had always been concerned about this threat and working hard, first to avert it, and since to recover from it).
Dr. Laska, a sociologist at the University of New Orleans and then director of the Center for Hazard Assessment, Research, and Technology (CHART), laid out the whole scenario. She touched on the growth in Louisiana population, the development of the Port of New Orleans and the offshore oil extraction and the associated refineries. She recounted a century of bad engineering along the Mississippi, the degradation of Louisiana’s coastal wetlands and the subsequent loss of their natural protection. She discussed the risks in depending upon evacuation as a strategy: the vulnerabilities of the lone evacuation route over Lake Pontchartrain and the fact that at any given time, 100,000 people would be too poor to find a ride, and 2000 people to sick to move. She estimated it would take 90 days to dry out the “bowl” (that portion of New Orleans under sea level and most vulnerable to flooding), and twenty years to recover. So far, as we say in our trade, that forecast seems to be verifying.

Read more

Beware the Wrath of a Presidential Storm

The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) may indeed have underestimated the danger that Typhoon Conson posed to Manila in July. But it seems even more likely that PAGASA director Prisco Nilo underestimated the political storm that ensued.
At an emergency disaster coordination meeting after the storm (known locally as Typhoon Basyang), President Benigno Aquino scolded Nilo because PAGASA had led Manilans to believe the capital would be spared the brunt of the rain and winds:

That [storm] information it is sorely lacking and we have had this problem for quite a long time. … You do what you are supposed to do… this is not acceptable. I hope this is the last time that we are all brought to areas different from where we should be.

“He really was not angry,” Nilo commented at a press conference. “It was just a comment made by a President, he wanted things to improve, that was his point.”  Yet it seems the president was indeed angry; angry enough to fire Nilo a few weeks later.
It was only the second week of Aquino’s term when Basyang hit metropolitan Manila on 13 July, initially as a weak Category 1 tropical cyclone. Heavy rains and flooding led to at least 100 deaths (at least 70 people were initially reported as missing). The 95 kph

Typhoon Conson (Basyang)
Typhoon Conson approaching the Philippines in July. Portents of political trouble.

winds caused also caused power and communications outages that paralyzed the city for days. PAGASA’s last advisory that night at 11:00 p.m. said that the typhoon had weakened and was headed farther north of Manila. Yet around midnight the eye of the storm passed through the area.
Nilo’s explanation to President Aquino was that the bureau’s equipment limited storm updates and that the system needed to be updated:

We update the bulletin every six hours to take into account possible changes that were not earlier indicated by the mathematical models we are using as guidance in coming up with our forecast.

According to the Philippine news service GMA News, others have spoken up about similar constraints on PAGASA:

PAGASA officials have repeatedly said lack of modern equipment is hampering them from doing their jobs more effectively.

President Aquino’s responded that the bureau should have consulted

Read more

Mt. Washington's World Record Wind Toppled

It stood for 62 years and helped earn New Hampshire’s 6,288-foot Mt. Washington the distinction of having the World’s Worst Weather. Yet, more than a decade ago, a little known tropical cyclone in the South Indian Ocean blew away Mt. Washington’s famous gust of 234 mph — the previous fastest wind ever measured on Earth outside of a tornado. According to the World Meteorological Organization (WMO), the record now belongs to Barrow Island, Australia, a spot of land 31 miles off that continent’s northwest coast that was blasted by Tropical Cyclone Olivia on April 10, 1996. Olivia delivered a record gust of 253 mph (408 kph).

Tropical Cyclone Olivia intensifies as it bears down on northwest Australia in April 1996. (Satellite image from the Japan Meteorological Agency, courtesy of Australia's Bureau of Meteorology.)

A panel of scientists charged with determining global weather and climate extremes as part of the WMO’s Commission for Climatology (CCl) recently reviewed numerous exceptional wind gusts recorded on Barrow Island during Olivia. They concluded that five peak gusts, ranging from 186 mph to the peak of 253 mph were indeed accurate. The other gusts measured 229 mph, 233 mph, and 215 mph, lending credibility to the record wind. The scientists concluded that a mesovortex in Olivia’s well-defined eyewall was likely the cause of the extreme winds.
But the record wind went unnoticed for a decade before the panel happened upon the observations from Barrow Island. Already stunned by losing the record wind gust distinction, Mt. Washington Observatory Executive Director Scot Henley told the Associated Press he was shocked the record remained hidden so long.
“Somehow it fell through the cracks and the Australians didn’t think it was a big deal,” he stated. “We hear that, and it kinds of blows our minds.”
Well, it might not have been quite as simple as that, as Jeff Masters of Weather Underground reports in his blog. He writes that Australia’s Bureau of Meteorology (BOM) was notified about the gusts, but considered them suspect since they were extraordinarily high for a 145 mph tropical cyclone, and because the accuracy of the equipment used to measure the gusts was unknown. Even after a paper on the extreme wind was written in 1999, the data remained in wait another 10 years until someone with the BOM resurrected it and brought it to the attention of the CCl. Read more about why it took 14 years for the record wind to be recognized.
The CCl panel determined the instrument that measured the record wind was a “heavy duty three-cup Synchrotac anemometer,” its report states. It was located near the center of Barrow Island and positioned 33 feet (10 m) above ground level and 210 feet (64 m) above sea level in relatively open terrain. Guy wires stabilized the cyclone-rated Hills telescoping mounting tower, and the anemometer was found to be regularly inspected and calibrated.
According to Wikipedia, Barrow Island, which is slightly larger than Brooklyn, New York, was uninhabited until the 20th century. Oil was discovered there in commercial quantities in 1964 and subsequent drilling resulted in Barrow Island becoming Australia’s leading producer of petroleum and natural gas.  The anemometer that measured the world’s new fastest surface wind is owned and maintained by Chevron.
A report of the record wind is posted on the Arizona State University Web site. It contains additional details of Olivia’s record event and names the report’s panel of experts within CCl.