Chapala Closing in on Yemen; Record November Warmth in Florida, Europe

A stretch of Middle Eastern coastline unaccustomed to tropical cyclones of any type is about to experience a full-blown landfall, as Cyclone Chapala bears down on the central coast of Yemen. Chapala held its intensity remarkably well on Sunday, thanks in large part to record-warm sea-surface temperatures and light wind shear. A large, solid central core of showers and thunderstorms (convection) helped Chapala barricade itself from the influence of extremely dry air from the Arabian Peninsula. Chapala remained a Category 3 cyclone on the Saffir-Simpson scale as of 15Z (10:00 am EST) Monday, with top sustained winds estimated at 110 knots (126 mph). Cloud-top temperatures have gradually warmed across Chapala’s convective shield, and the storm has become more asymmetric in recent hours. Dry air will be infiltrating the storm more rapidly as it nears landfall, but with other conditions largely favorable, Chapala has a good chance of making landfall at Category 1 strength. Chapala swept to the north of the remote island of Socotra on Sunday night, triggering a flurry of photos and videos on social media--at least some of which were bogus, underscoring the need to double-check sources as this rare event unfolds. Al Jazeera reports that Chapala caused at least two deaths and nine injuries on Socotra, with more than 100 homes destroyed.


Figure 1. Enhanced infrared image of Cyclone Chapala, with the storm track overlaid. Icons denote Chapala’s predicted strength on the Saffir-Simpson scale. Chapala is projected to be a weakening Category 2 strength cyclone about six hours before landfall.


Figure 2. Steep hillsides surround the city of Mukalla on the central Yemen coast. Image credit: Google Images, via Stu Ostro, The Weather Channel.

Catastrophic rains possible near major Yemen city
The parched Yemen coast is nearly devoid of population centers, but Chapala is aiming for one of them. The forecast track from the Joint Typhoon Warning Center as of 10:00 am EST Monday (7:00 pm Yemen time), in close agreement with the scant model guidance available, brings Chapala into the coast about 50 miles south of Mukalla (also Al Mukallah) on Tuesday night local time, putting that city of 300,000 on the more dangerous right-hand side of the cyclone. The potential storm surge will be tempered somewhat by the steep rise of the undersea topography just offshore, but this region’s experience with any surge is very limited. According to a review paper by storm surge expert Hal Needham, there are only four observations in the scientific literature of storm surge or storm tide in the Arabian Sea. The only other hurricane-strength cyclone in modern records to affect the Arabian Peninsula is 2007’s Cyclone Gonu, which nicked the southeast corner of the peninsula en route to Iran. Water levels during Gonu reached 5 meters (16 feet) at Ras al-Hadd, Oman, although that total may include waves as well as storm surge.

Chapala’s landfall may be far enough southwest to spare Mukalla from hurricane-force winds. However, there is a far bigger threat: Chapalla’s path is virtually certain to bring torrential rain to Mukalla and the surrounding mountains, raising the spectre of potentially disastrous floods and mudslides. The counterclockwise circulation around Mukalla will pull dry air into the cyclone’s south side but will keep moist air flowing into the north side, where the heaviest rains will fall. Amount could easily top one to two feet of rain in some areas, representing a number of years’ worth of rain in this desert regime. The immediate coast averages less than 2” of rain per year.

It is difficult to overstate the rarity and gravity of this event: a hurricane-strength storm striking near a large, ancient city, situated near mountains, with no modern experience in dealing with tropical cyclones. Although Hurricane Patricia got much more media attention, Chapala may end up bringing more damage and misery by far. The ongoing civil war in Yemen can only exacerbate the suffering of those affected and complicate relief efforts. “The humanitarian situation in Yemen is deteriorating rapidly,” reported the UN Office for the Coordination of Humanitarian Affairs in an October 15 update. We can only hope that the powers that be respond to this threat in line with its seriousness.


Figure 3. 5-day rainfall totals projected by the HWRF model run for Cyclone Chapala for the period starting at 06Z (1:00 am EST) Monday, November 2, 2015. The heaviest rains--perhaps 24” to 32” or more--are projected to fall close to the city of Al Mukallah, just to the right of Chapala’s path. Image credit: NCEP/EMC.


Figure 4. Average annual rainfall in Yemen. Image credit: CIA, via Perry-Castañeda Library Map Collection, University of Texas at Austin.


The autumn heat is on in eastern U.S. and Europe
Torrential rains progressed over the weekend from Texas into the Southeast, where the western Florida Panhandle has been especially hard-hit. CoCoRaHS observations for the 24 hours ending at 7:00 am EST Monday topped 7” at one site in Walton County, and flash flood watches remained in effect at midday Monday from Florida to North Carolina.

Downstream of the heavy storms, Sunday and Monday have felt more like midsummer than mid-autumn across most of Florida. In Tallahassee, Sunday’s high temperature of 88°F and low of 75°F both tied for the warmest ever recorded there in November, and the day’s average of 81.5°F handily beat the November record of 80.5°F set on 11/11/82 (records extend back to 1892). At midnight, it was still a sultry 80°F, with a relative humidity of 87%! Tallahassee’s overnight low on Sunday night was a ridiculous 78°F, but the rains should move in later today, tamping down that reading before midnight. (Thanks to Jedkins01 for calling attention to the Tallahassee warmth.) As the front retreats north ahead of a strong upper-level trough in the West, mild, moist air will overspread most of the eastern half of the country. In parts of southern Minnesota, Wisconsin, and Michigan, nighttime lows could stay above 55°F (warmer than the average daily highs) by midweek.

Balmy temperatures are also gracing much of Europe for the first week of November, thanks to an unusually strong upper-level high. On Sunday, the United Kingdom saw its warmest November temperature in more than a century of official records, as Trawscoed, Wales, soared to 22.4°C (72.3°F), besting the previous mark of 21.7°C (71.1°F) set in the Wales town of Prestatyn on November 4, 1946. On Monday afternoon, Trawscoed warmed again to at least 21.2°C (70.0°F), based on hourly observations.

Temperatures this week will be especially mild for mid-autumn across northern latitudes and higher altitudes of Europe. Finland saw its warmest-on-record November temperature on Monday with 13.3°C (56.0°F) at the town of Jomala, which held the previous national record of 13.0°C (November 12, 1999). In Helsinki, Finland, where the all-time November record is 11.6°C (52.9°F). Helsinki’s Vantaa airport likely topped that reading on Monday, with the highest Celsius-rounded hourly observations hitting 12°C (53.6°F). The latest WU forecast calls for a high of 55°F in Helsinki on Tuesday. The town of Sunndalsøra, Norway--less than 300 miles south of the Arctic Circle--reached at least 64°F on Monday. Later this week, temperatures may inch above freezing and trigger snowmelt at altitudes as high as 4000 meters (13,100 feet) in the Alps, according to international weather records historian Maximiliano Herrera, who maintains a comprehensive list of extreme temperature records for every nation in the world on his website.

WU blogger Steve Gregory outlines the potential for continued warmth into mid-month across eastern North America, plus the latest on El Niño, in his post today.

Bob Henson