The low pressure area we have been following tracking toward the Windward Islands the last several days has become Tropical Storm Bertha Thursday night. Showers and thunderstorms increased around the center of the low pressure early Thursday night and Bertha was born. The system has about another 12 to 18 hours of low shear in order to continue to develop and strengthen. This lower shear is what is allowed the showers and storms to form closer to the center of the low this evening. It is still battling dry air, but that dry air will most likely only act to limit the strength and size of Bertha.
A U.S. Air Force reconnaissance C130 aircraft investigated the low pressure area Thursday afternoon. Surface winds at that time north and northeast of the low center were estimated at 40-45 mph, which was strong enough for the system to be classified as a tropical storm. But these winds were found well north and northeast of the low level center. Thunderstorm development at that time was well displaced from the center. This is the reason the low was not upgraded to a depression or tropical storm earlier Thursday.
Bertha will now most likely continue as a Tropical Storm the next few days and will track into the northern Windward Islands Friday evening then pass over or near Puerto Rico Saturday into Saturday evening. This will bring gusty winds and showery rainfall over the northern Windward Islands and the Leeward Islands Friday night and into the Virgin Islands and Puerto Rico Saturday.
Tropical Storm warnings are in effect for for Barbados, St. Lucia, and Dominica. A tropical storm watch is in effect for Puerto Rico, Vieques, Culebra, the U.S. Virgin Islands, and St. Vincent and the Grenadines.
Bertha, as of 11 pm Thursday, was centered abour 275 miles east southeast of Barbados and was moving west northwest at 20 mph. Maximum sustained winds are 45 mph.
Tropical Storm conditions are first expected to reach the areas under warnings midday Friday. The areas under the tropical storm watch may experience the tropical storm conditions Saturday. In general, rainfall of 1-3 inches is expected with isolated amounts to 5 inches. This rain can cause flooding. Additionally, higher waves and surf will impact areas near the track of Bertha.
The storm will track over or just east of the Turks and Caicos Islands during Sunday and near the eastern Bahamas Monday. The more reliable computer forecasts show Bertha staying a low end tropical storm through early next week. This is due to more hostile upper level winds beyond Friday night, the overall dry air, and the interaction with land masses along its path. No major changes in strength of the system are forecast in the near term, and it could eventually weaken back below tropical storm status.
So, all in all, we have Tropical Storm Bertha but its strength should remain in check on its trek from the Windward Islands later Friday to to near the eastern Bahamas Monday then northward over the Atlantic Tuesday. That track should be far enough to the east of the United States to have no impacts on Florida or South Carolina through Monday. The coast of North Carolina may come into play as far as some effects sometime Tuesday or Tuesday night, but that is something to watch for now.
The rest of the Atlantic Basin remains relatively quiet
By AccuWeather Senior Meteorologist Dave Houk
803 ABNT20 KNHC 312342 TWOAT TROPICAL WEATHER OUTLOOK NWS NATIONAL HURRICANE CENTER MIAMI FL 800 PM EDT THU JUL 31 2014 For the North Atlantic...Caribbean Sea and the Gulf of Mexico: An Air Force Reserve reconnaissance aircraft this afternoon and evening investigated the well-defined low pressure system located about 350 miles east-southeast of Barbados, and found surface winds of 40 to 45 mph across the northern and eastern portions of the circulation. Showers and thunderstorms have increased east of the center during the past couple of hours, and if this development trend continues a tropical storm could form later tonight or early Friday. Regardless of development, gale-force winds are likely to spread across portions of the central Lesser Antilles beginning by midday Friday. Interests in these areas should continue to monitor the progress of this disturbance as it moves west-northwestward near 20 mph, since watches or warnings could be required for some of these islands later tonight or Friday. * Formation chance through 48 hours...high...80 percent. * Formation chance through 5 days...high...80 percent. $$ Forecaster Stewart