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Good evening everyone!
Well, the NHC kinda jumped the gun…ENTER TROPICAL STORM (?) BERTHA…
As of the 11:00 p.m. EDT Advisory issued from the NHC, the following information was available on newly formed Tropical Storm Bertha:
11:00 PM AST Thu Jul 31
Location: 12.3°N 55.5°W
Moving: WNW at 20 mph
Min pressure: 1008 mb / 29.77 in
Max sustained: 45 mph
Bertha continues to move to the WNW as posted earlier, around the southern periphery of the subtropical ridge. The WNW motion is being induced by the weakness in the ridge noted over the area of the Bahamas. I expect this WNW motion to continue for the next 60 – 72 hours, but gradually becoming more of a 300 – 305 degree track during this time. Thereafter, a turn toward the NW should occur. Based on analysis of the most available Steering Layers Forecast maps, I do not anticipate Bertha posing a direct threat to the SEUS as she eventually should recurve away from the U.S. I will be monitoring this past the 5 day track to keep tabs on the steering pattern. I concur with the NHC track, which is inline with the middle of the suite
Tropical Storm Watches and Warnings have been issued, and residents in the Lesser Antilles and Puerto Rico. Residents should take the necessary preparations for their areas.
The NHC upgraded the system based on a “band” of convection that moved in toward the center earlier, NOTED AT THE VERY BEGINNING OF THE SATELLITE LOOPS. Stewart is one of my favorite forecasters, and is one of the best at the NHC, however I have to disagree at that moment with the designation…solely based on the NHC criteria of a Tropical Cyclone, and various correspondence with NHC indicating deep convection should be persistent for at least 24 hours. By definition from the NHC:
Tropical Cyclone:A warm-core non-frontal synoptic-scale cyclone, originating over tropical or subtropical waters, with organized deep convection and a closed surface wind circulation about a well-defined center. Once formed, a tropical cyclone is maintained by the extraction of heat energy from the ocean at high temperature and heat export at the low temperatures of the upper troposphere. In this they differ from extratropical cyclones, which derive their energy from horizontal temperature contrasts in the atmosphere (baroclinic effects).
However, I do agree with him in a good point he brought out in the Forecast Discussion:
The environment surrounding Bertha is not particularly favorable for significant strengthening during the next two days due to modest westerly shear and limited mid-level moisture. However, the cyclone will be moving over increasing SSTs and within an upper-level atmosphere that is slightly cooler than normal. The resultant increase in instability could allow for some slight strengthening to occur before Bertha interacts with Puerto Rico and eastern Hispaniola in about 48 hours or so.
What this effect does..is increases the ELR (Environmental Lapse Rate), which allows for instability and rising air for condensation to occur. Based on my analysis of current and forecast wind shear products, Bertha is entering an area of increased shear, however based on the shear forecast, and as mentioned in the NHC forecast discussion, upper level winds are forecast to become more conducive for some slight strengthening over the next 48 hours. Based on these thermodynamic parameters, I concur with the NHC intensity forecast through the 120 hour time frame.
I will have another update sometime tomorrow morning.
Have a blessed evening.
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST / SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS
OFFICIAL SKYWARN SPOTTER (ADVANCED)