Tropical Cyclone Chapala, the second strongest storm on record for the Arabian Sea, is holding its own as it continues plowing westward toward Yemen. As of 8:00 am EDT Saturday, Chapala’s top sustained winds were down to 135 mph, at the other end of the Category 4 scale from the peak of 155 mph observed on Friday. After its structure was somewhat disrupted on Friday, perhaps by dry air intruding into its circulation, Chapala appears to be regrouping, with a solid inner core of convection and a distinct eye 10 miles in diameter.
Figure 1. Tropical Cyclone Chapala as seen from the International Space Station at sunset on Halloween evening, October 31, 2015. At the time, Chapala was a Category 4 storm with 135 mph winds. The coast of Oman/Yemen is visible at the bottom of the image. Image credit: Commander Scott Kelly.
Figure 2. Tropical Cyclone Chapala as seen by the MODIS instrument on NASA's Terra satellite on Saturday morning, October 31, 2015. At the time, Chapala was a Category 4 storm with 135 mph winds. Image credit: NASA.
The forecast for Chapala The biggest change since Friday is a southward departure in Chapala’s track. The cyclone is now heading due west and should continue on that bearing for the next couple of days, with a slight curve to the west-northwest as it approaches Yemen on Monday night. Chapala’s healthy structure may keep dry air at bay for some time, but eventually the cyclone should weaken as it near the Arabian Peninsula and ingests greater amounts of parched desert air. The Joint Typhoon Warning Center brings Chapala onshore in the high tropical-storm-strength range, with sustained winds possibly close to hurricane strength.
Figure 3. Three tropical cyclones are known to have made landfall on the southern coast of Oman and Yemen betwen 1891 and the beginning of modern satellite records (1990). Two of these reached northeast Yemen, in May 1959 and May 1960. Both were rated as “severe cyclonic storms” prior to landfall (solid line), meaning their top 3-minute average wind speeds were at least 48 knots (55 mph). Image credit: Courtesy Dr. Mrutyunjay Mohapatra, Head, Cyclone Warning Division and Regional Specialised Meteorological Centre, India Meteorological Department.
According to NOAA's Historical Hurricanes tool, there have only been six major Category 3 or stronger tropical cyclones recorded in the Arabian Sea (though accurate satellite records go back to just 1990.) The Arabian Sea doesn't get many tropical cyclones since it is small; furthermore, the Southwest Monsoon keeps the tropical cyclone season short, with a short season that lasts from May to early June before the monsoon arrives, then another short season in late October through November after the monsoon has departed. Strong Arabian Sea storms are rare due to high wind shear and copious dry air from the deserts of the Middle East, with just two Category 4 or 5 storms ever recorded--Gonu in 2007 and Phet in 2010. Both cyclones hit Oman after weakening below Category 4 strength.
Landfalling cyclones are even more rare in Yemen. The only one in the post-1990 satellite database is Tropical Depression Three of 2008 (also known as the 2008 Yemen Cyclone), which came on the heels of heavy rains from another storm and resulted in disastrous flooding. According to EM-DAT, the international disaster database, that storm killed 90 people and did $400 million in damage, making it the second worst natural disaster in Yemen's history, behind a June 13, 1996 flood (thanks go to wunderground member TropicalAnalystwx13 for alerting us to this fact.) The India Meteorological Department maintains a database of tropical cyclones in the region going back to 1891 that shows two cyclonic storms reaching the Yemen coast in 1960 and 1961 (see Figure 3).
Chapala’s southward track will make it only the second tropical cyclone recorded near the mouth of the Gulf of Aden, which is crossed by roughly 400 ships a week. The adjustment in Chapala’s track could have major implications for Yemen, as it brings the center closer to the 980-year-old settlement of Al Mukalla (also known as Mukalla), a busy port and Yemen’s fifth-largest city (population around 300,000). If Chapala were to pass just south of Al Mukalla, the sharp angle of approach to the coast would accentuate any storm surge. Yemen has been in the grip of a civil war since March, so any landfall near this populated area could intersect with the conflict in hard-to-predict ways. According to an October 30 article from Reuters, ten of Yemen's 22 governorates were assessed as being in an emergency food situation in June, one step below famine on a five-point scale. The assessment has not been updated since then, partly because experts have not managed to get sufficient access to survey the situation. About a third of the country's population, or 7.6 million people urgently require food aid, the The U.N. World Food Programme said (thanks go to wunderground member barbamz for alerting us to this article.)
As it moves ashore, Chapala will slam into steep mountains near the coast, boosting its potential to dump several years’ worth of rain in just a day or two (see Figure 6). The annual average rainfall in Yemen is less than 2” along the immediate coast and less than 5” inland, except along higher terrain, where it can approach 10”. Any landfall near Al Mukalla could result in serious urban flooding (the city straddles a canal that extends to the coast from the adjacent mountainsides).
Figure 6. The 5-day rainfall forecast from the 2 am EDT Saturday, October 31, 2015 run of the HWRF model called for some truly stunning rainfall amounts in the parched desert regions of eastern Yemen: over two feet! Image credit: NOAA/EMC.
Rain-weary Texans deal with another deluge Yet another round of epic downpours struck the heart of Texas from Friday into Saturday. The focus on Friday morning was the HIll Country and the adjacent San Antonio and Austin metro areas, which suffered through record rain and destructive flooding back in May. The air traffic control center at Austin’s Bergstrom International Airport has been shut down after being inundated with six inches of water on Friday. A Houston center is handling its duties until a temporary facility arrives on Monday. Bergstrom received 5.76” of rain in just one hour, as part of a phenomenal calendar-day total of 14.99” on Friday. That’s more than the site had ever recorded in any prior 14-day period! (Records at Bergstrom go back to 1942. Thanks to Nick Wiltgen at weather.com for this statistic.). The total also came within a hair (0.067%) of reaching the city’s all-time 24-hour record of 15.00”, set at Camp Mabry on September 9, 1921, in association with a Category 1 hurricane that caused severe flooding in the San Antonio area. Further south, Brownsville had its second wettest October day in 128 years of recordkeeping, with 6.55” on Friday beaten only by 9.09” on October 4, 1996, in association with Tropical Storm Josephine. The absence of a tropical cyclone makes this event across central and south Texas all the more remarkable.
Figure 7. Jim Richardson and his wife Jeannette look on as the Blanco River recedes after the flash flood in Wimberly, Texas Friday, Oct. 30, 2015. A fast-moving storm packing heavy rain and destructive winds overwhelmed rivers and prompted evacuations Friday in the same area of Central Texas that saw devastating spring floods. Image credit: Ricardo Brazziell/Austin American-Statesman via AP.
A subsequent round of heavy thunderstorms moved into southeast Texas overnight and into Saturday morning, causing widespread flooding in the Houston area, as well as scattered wind damage perhaps associated with one or more tornadoes. With light rain hanging on at noon CDT Saturday, Houston’s Hobby Airport had received 6.50” for the day, bringing its monthly total to 14.24”. Hobby will fall short of the Houston area’s wettest October on record, 17.64” in 1949, a total largely goosed by a Category 2 hurricane early that month. The front edge of this sprawling area of heavy thunderstorms is now approaching southeast Louisiana, which has also been hammered by heavy rain in October. Baton Rouge had received 10.85” for the month as of Friday, and New Orleans 8.88”. NOAA’s Weather Prediction Center is calling for as much as 5-6” of rain over the area today into Sunday. Baton Rouge has an outside chance of scoring its wettest October on record (17.64”, from 1949; records go back to 1889), as does the Louis Armstrong New Orleans International Airport (13.20” in 1985, in association with Hurricane Juan; records go back to 1946).
Dallas-Fort Worth International Airport racked up another 2.25” from Friday through 11:00 am CDT Saturday. The airport has now recorded 48.92” for the year, making 2015 the sixth wettest year since DFW-area records began in 1898. One of the most reliable U.S. impacts from El Niño is increased cold-season rainfall from Texas to Florida. Given the strong El Niño influence already at hand, DFW has a good chance over the next two months of topping 53.54” (1991) to score its wettest year on record. In fact, it could happen quite soon: WPC is projecting 2” to 5” of rain across central North Texas late next week, as another strong Pacific upper-level storm carves its way into the western U.S. That storm will give the Pacific Northwest a seasonally heavy drenching this weekend, and it may leave the first significant accumulation of the season along the snow-starved Sierra Nevada on Monday and Tuesday--perhaps as much as a foot on the highest peaks. A winter storm watch has been hoisted for the region, but we’re guessing most residents will be elated rather than spooked by this October 31 development. Have a great Halloween weekend, everyone!
Bob Henson and Jeff Masters
VIDEO: Cecilia Parker's husband sent this video before his car was swept away. He's being rescued from a tree. pic.twitter.com/4nxYdz852c
Video 1. This powerful video was taken by a motorist in central Texas on Friday morning, October 30, 2015, shortly before he awaited rescue. Once a car is afloat in moving water, it will generally flow toward the deepest, fastest-moving areas. According to NOAA, it only takes two feet of moving water to float most vehicles. Image credit: KVUE News.
Video 2. Technician Derek Urch from NWS/Brownsville captured this lightning strike of the WSR-88D Radar, which knocked radar data out completely during a flash flood event on Friday, October 30, 2015. Image credit: NWS/Brownsville.