Erika takes aim at Florida after killing 20 in Dominica

Tropical Storm Erika continues to struggle to remain a tropical cyclone as it battles a hostile environment in the Caribbean Sea.

(MORE: Heart of the Hurricane Season is Here)

Satellite imagery continues to show Erika's convection (thunderstorms) displaced east of the center of circulation. At the same time, the center of circulation is ill-defined and has continued to trend south of previous National Hurricane Center forecasts. This is a common pattern for a struggling tropical system, as Danny did the same thing earlier this month.

Land interaction with the higher terrain of Haiti and the Dominican Republic has likely further degraded Erika's circulation. Pico Duarte on the Dominican Republic is over 10,000 feet and Haiti has several peaks over 7,000 feet. Now Erika's apparent center will have to track over parts of Cuba.

Strong westerly to southwesterly wind shear has been consistently very strong, compared to average, in the Caribbean Sea this hurricane season, so far. Erika will continue to be hammered by this environment of higher wind shear over the next day or so.

The result is that it is uncertain how much longer the storm will remain classified as a tropical cyclone. The official National Hurricane Center forecast now weakens Erika to a tropical depression later Saturday, and if reconnaissance aircraft fails to find a closed circulation (in other words, sufficient westerly suface winds on Erika's southern flank), Erika could officially be declared a remnant or tropical wave, after which the NHC would no longer issue advisories and all watches/warnings would be dropped.

But that doesn't mean there may not be serious impacts. Regardless of Erika's tropical status and organization, locally heavy rain and flash flooding will continue to be threats in the days ahead.

Intense rainfall impacted the Dominican Republic on Friday, with a personal weather station in Barahona reporting over 24 inches of rain. That station also reported an astonishing 8.80 inches of rain in one hour from 8 p.m. to 9 p.m. Friday.

A band of torrential rain also resulted in deadly flash flooding on the island of Dominica in the Lesser Antilles, Thursday. Roads were washed out, homes were damaged and an airport flooded.

Canefield Airport near the capital of Roseau, Dominica, picked up 12.64 inches (322.4 millimeters) of rain in a 12-hour period ending just before 2 p.m. EDT Thursday.

Bands of locally heavy rain currently over Haiti will shift to parts of Cuba, Jamaica and the possibly the Bahamas by late-day Saturday.

Despite the long-term Caribbean drought, rain rates of several inches per hour could trigger flash flooding and mud/rockslides. Historically, some of the highest death tolls with Caribbean tropical cyclones have occurred in these situations.

The National Weather Service in San Juan, Puerto Rico, said some parts of the island had already picked up 3 to 4.5 inches of rainfall in Erika's rainbands as of early Friday morning.

Tropical storm force winds were reported across portions the U.S. Virgin Islands on Thursday, with that shifting west on Friday. Barahona, Dominican Republic was gusting up to 52 mph as of late Friday evening. The highest measured gust so far in the Caribbean was 62 mph at St. Croix Thursday evening. St. Thomas registered a gust to 48 mph. The peak gust in San Juan, Puerto Rico, on Friday was only 33 mph. Some gusts to 50 mph were measured over the higher terrain of Puerto Rico Friday, according to NWS-San Juan.

Erika may continue to produce tropical storm force winds, mainly in gusts, primarily on the east and north sides of its circulation.
As it stands, the forecast continues to contain a large amount of uncertainty with Erika. The system may not survive the hostile environment in the vicinity of Cuba on Saturday, as we mentioned above.

For now, potential impacts in the Bahamas from Erika are focusing on the southern and western most islands, with eastern Cuba taking more of a direct hit, and heavy rain also possible in Jamaica. No new warnings have been issued west of the Bahamas, mainly due to the challenging intensity forecast.

(FORECAST: Nassau | Turks & Caicos)

Here are the two most plausible scenarios regarding Erika right now:

Erika survives: If Erika survives the hostile environment through Saturday, it could pass near the Florida Keys on Sunday, then track northward in the eastern Gulf of Mexico and landfall somewhere in Florida several days from now. In this scenario, Erika would have very little time to re-strengthen over the warm water north of Cuba before affecting the Keys, but then have a small chance of acquiring a little strength before its final Florida landfall.
Erika fizzles: If Erika remains disorganized, it may tend to stay on a westward or west-northwest heading, instead of turning north of Cuba. In this scenario, Erika may dissipate entirely to a tropical wave sometime Saturday.

Regardless of the scenario, steering currents in the upper atmosphere would still bring a moisture surge, and attendant threat of locally heavy rainfall into Florida and parts of the Southeast in the days ahead.

All interests in The Bahamas, Cuba, Florida and the rest of the eastern Gulf Coast should continue to monitor the progress of Erika. The past few days have proven that even a weak tropical system can still cause significant destruction, particularly in terms of flash flooding.

源：http://www.aol.com/article/2015/08/29/erika-struggles-but-still-soaks-the-caribbean/21229033/?icid=maing-grid7|main5-news|dl2|sec1_lnk2%26pLid%3D1695147642