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Will Erika Survive its Traverse of Hispaniola?

By: Jeff Masters 3:45 PM GMT on August 28, 2015

Tropical Storm Erika is headed into the teeth of Hispaniola's 10,000-foot high mountains, as the storm marches west-northwest at 17 mph, spreading torrential rains and sustained winds of 50 mph along its path. The biggest danger of the storm to the islands is heavy rainfall; according to the Antigua Met Service, Canefield Airport on Dominica recorded 12.62" (320.6 mm) of rain in twelve hours on Wednesday night and Thursday morning from Erika, and the resulting heavy flooding has killed at least twelve people.

Video 1. Floodwaters rage through a street on Dominica island in the Caribbean on Thursday, August 27, 2015, after Tropical Storm Erika dumped 12+" of rain on the island.

An Air Force hurricane hunter aircraft was in the storm Friday morning, and found Erika continued to have a large area of tropical-storm force winds up to 50 mph to the southeast of the center. A Personal Weather Station (PWS) in southwest Puerto Rico at Barrio Hoconuco at higher elevation recorded wind gusts up to 56 mph Friday morning. Punta Cana, on the eastern tip of the Dominican Republic, had a wind gust of 40 mph at both 10 am and 11 am AST. Rainfall as of 11 am EDT Friday over Puerto Rico had mostly been below 2", according to estimates from the San Juan radar.

Figure 1. MODIS image of Erika from NASA's Aqua satellite taken at approximately 11 am EDT Friday August 28, 2015. At the time, Erika had top sustained winds of 50 mph. Image credit: NASA.

Satellite loops on Friday morning showed that Erika continued to be disorganized in the face of dry air and wind shear. There is not much heavy thunderstorm activity on the storm's north side, where there was dry air from the Saharan Air Layer, though there was a vigorous area of heavy thunderstorms on its southeast side. These thunderstorms did not change much in intensity or areal coverage on Friday morning. Wind shear due to upper-level winds out of the west was a high 20 - 25 knots, and this shear was driving dry air on the northwest side of Erika into its core, disrupting the storm.

Figure 2. Latest long-range radar image of Tropical Storm Erika from the San Juan, Puerto Rico radar.

Figure 3. Predicted rainfall for Erika for the 126-hour period ending at 8 am EDT September 2, 2015, from the 06Z (2 am EDT) Friday August 28, 2015 run of the HWRF model. This rainfall swath is likely displaced too far to the east, and will probably be centered directly over Florida. Rainfall amounts of 4 - 8" can be expected in many areas along Erika's path, with a few areas of 8+" (bright yellow colors.) Image credit: NOAA.

Will Erika survive Hispaniola?
Erika's battle against dry air and high wind shear has caused the center of the storm to reform several times to the south of its original position, closer to the storm's heaviest thunderstorms. These southward shifts mean that Erika is now poised to track directly over mountainous Hispaniola island, whose highest peak exceeds 10,000 feet in height. This encounter will not go well for Erika, particularly since wind shear will remain a high 15 - 25 knots during the traverse, and dry air will continue to wrap into Erika's circulation during the crossing. These combined factors could lead to Erika's dissipation by Saturday morning. The traverse of the island may also cause the center to reform to the west of the island, which would then mean that Erika would encounter some of the high terrain of eastern Cuba. If Erika survives into Saturday morning, which I give a 50% chance of occurring, the storm may have time to intensify into a strong tropical storm with 60 mph winds before hitting South Florida. If Erika dissipates over Hispaniola Friday night, the storm could still reorganize into a minimal-strength tropical storm with 40 mph winds before encountering South Florida. The upper low over Cuba that is bringing high wind shear to Erika today is forecast to weaken on Sunday, which should cause wind shear to drop to the moderate range, 10 - 15 knots, which would allow some modest strengthening of Erika. A trough of low pressure will turn Erika to the north on Monday, and it is possible this turn will occur just west of the Florida, bringing Erika northwards along the west coast of Florida and into the Florida Panhandle by Tuesday--as suggested by the 00Z Friday (8 pm EDT Thursday) runs of the European and UKMET models. Regardless, much of Florida can expect heavy flooding rains from Erika Sunday through Tuesday.

Figure 4. Drought conditions in the Caribbean during July 2015 as estimated via satellite. Drought is indexed here using the 6-month Standard Precipitation Index (SPI), a measure of how much rainfall has occurred in the previous six months compared to average. Drought is common in the Caribbean during El Niño years, due to an atmospheric circulation that brings plenty of dry, sinking air and high pressure to the region. The last major drought in the Caribbean was in 2010, which also had an El Niño event. Image credit: NOAA Global Drought Portal.

Erika's rains to help alleviate record Caribbean heat and drought
Record heat and drought has been widespread over the Caribbean this summer, with the worst drought conditions occurring over Haiti, Eastern Cuba, Nicaragua, Panama, Colombia, Venezuela, Honduras, and Costa Rica. Reuters reported today that Cuba will begin a two-month cloud-seeding campaign over the eastern part of the Caribbean island in hopes of easing its worst drought since at least 1901. The dry conditions and associated atmospheric circulation that has brought warm, sinking air and high pressure to the region has led to many Caribbean cities recording their all-time highest temperatures on record. According to weather records researcher Maximiliano Herrera, on Thursday, the Observatory in Santo Domingo, the capital of the Dominican Republic, hit 99°F (37.2°C), the hottest temperature ever recorded in the city (previous record: 37.0°C on August 17, 1947.) This record high was aided by the fact that dry, sinking air due to the outflow from Tropical Storm Erika was over the Dominican Republic. Another big factor in the yesterday's record high, and the record highs all across the Caribbean this year, is the fact that the year-to-date period of 2015 has been the warmest on record for the globe as a whole. Here is Mr. Herrera's list of cities in countries bordering the Caribbean that have set all-time heat records this year:

Cienfuegos (Cuba) max. 37.0°C July 6
Jucaro (Cuba) max. 36.8°C July 10
Jucaro (Cuba) max. 37.0°C July 28
Contramaestre (Cuba) max. 38.2°C July 29
Isabel Rubio Airport (Cuba) max. 36.3°C July 29
Indio Hatuey (Cuba) max. 38.1°C July 30
Havana (Cuba), max. 37.0°C, April 26
Holguin (Cuba), max. 38.7°C, April 26
Guaro (Cuba), max. 38.0°C, April 26
Contramaestre (Cuba), max. 37.7°C, April 27
Velasco (Cuba), max. 38.6°C, April 28
Ciego de Avila (Cuba), max. 38.0°C, April 28
Puerto Padre (Cuba), max. 38.4°C, April 29
Punta Lucrecia (Cuba), max. 37.3°C, April 29
Nuevitas (Cuba), max. 38.5°C, April 30

Riohacha (Colombia) max. 40.6°C July 13
Cartagena, Colombia, max. 40.4°C,  June 24
Santa Marta, Colombia, max, 38.6°C, June 24
Arjona, Colombia, max, 40°C, June 24
Urumitia, Colombia, max, 42.0°C, June 27
Riohacha, Colombia, max, 40.0°C, June 29

Merida (Mexico), max. 43.6°C, April 26

Tela (Honduras), max. 40.6°C, April 28

Coro (Venezuela), max. 43.6°C, April 29 (New all-time national record high for Venezuela)

Dominican Republic
Santo Domingo (Dominican Republic), 37.2°C, August 27

U.S. Virgin Islands
Charlotte Amalie (U.S. VI), 35°C (95°F), August 1 (all time high for the station and the U.S. Virgin Islands)

New tropical wave moving off the coast of Africa
A strong tropical wave will move off the coast of Africa on Saturday, and has the potential to become a tropical depression next week as it moves west-northwest near or over the Cape Verde Islands at 10 mph. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave the wave 5-day odds of development of 30%. This wave will likely move too far to the northwest to be a threat to the Caribbean islands.

Hurricane Ignacio a threat to Hawaii
Hurricane Ignacio continues to slowly intensify in the waters to the east-southeast of Hawaii, and could pass within 200 miles of Hawaii on Tuesday. Satellite loops on Friday morning showed that Ignacio had an impressive area of heavy thunderstorms, but no eye was apparent. Ignacio is over warm waters with light to moderate wind shear, conditions that favor continued intensification. Hawaii should also keep an eye on Hurricane Jimena, which is intensifying rapidly in the waters over 1500 miles east southeast of the islands. Jimena is expected to top out at Category 4 strength on Sunday, but eventually recurve to the north well before reaching Hawaii. In about ten days, Jimena has the potential to traverse ocean areas off the coast of Northern California where no tropical storm has ever been observed.

Bob Henson or myself will have another Erika post later today.

Jeff Masters


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