United States: The South American/Andean Cold Surge continues to race through Peru and the west, central and east Amazon basin of Brazil. It has already crossed 5S and will cross the Equator tonight. You can see the large arcing area of showers and thunderstorms it is producing from east to west.
The showers and thunderstorms ahead of the surge will reach the coastal areas and Guianas Thursday (GFS shows best chance for thunderstorms Friday) they reach the southern islands later Thursday and central islands by Friday.
The cool air will be modified and warm when it passes over the still very warm seas so the islands will not see much change in temperature except those closer to South America like inland Trinidad areas 1 or 2 nights. Guianas will feel a bigger change in temperature.
2nd pic: The NHC has now seen enough evidence from the models that something can develop (20% chance) somewhere in the Caribbean Sea and/or SW Atlantic from the large areas of convergence and spin that the cold surge will help spark.
An upper trough/low will also set up to the north around the Bahamas to Hispaniola and on its south and east side will cause the steering flow to be from SW to NE sending rainfall and any system that forms to the NE.
The GFS shows 1 low pressure forming from the cold surge in the SW Caribbean Sea and also another within a broad area of upper trough enhancement in the East Caribbean Sea. It shows the bulk of heaviest rainfall moving into the northern islands with the Lesser Antilles also receiving enhanced rainfall. For a sample of this, see 3rd pic of GFS average RH and wind between 700-300mb(10-30k feet) for Saturday.
Edit: The Euro model also shows enhanced rainfall for the Eastern Caribbean islands from late Thursday to next Tuesday and best chance for heavy being Saturday to Sunday.
