The Andean/South American cold surge in Colombia/west Venezuela is generating large clusters of thunderstorms with very cold cloud tops tonight. The cold air is pushing moisture up onto the eastern-facing flanks of the northern Andes, thus causing tremendous uplift and rainfall.
There are also likely locally severe winds. These large clusters of thunderstorms will activate a low pressure in the SW Caribbean Sea next 24-48 hours. The northern Andes are tall but not as tall as those further south and allow enough gaps for moisture to flow over to the west and NW.
On the eastern side of the surge, clusters of thunderstorms are impacting east Venezuela/West Guyana and southern Suriname. On overnight Thursday to Friday, models indicate more thunderstorm coverage in the Guianas.
The South American/Andean Cold Surge continues to race through Peru and the west, central and east Amazon basin of Brazil( See 1st pic). 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 the best chance for thunderstorms Friday) …. they will reach the southern islands later Thursday and the 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 closest to South America, like inland Trinidad areas, for 1 or 2 nights. Guianas will feel a bigger temperature difference.
The NHC has now seen enough evidence from the models that something can develop(20% chance) somewhere in the Caribbean Sea and 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 one low pressure from the SW Caribbean Sea’s cold surge and another within a broad area of upper trough enhancement in the eastern 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 the best chance for heavy being Saturday to Sunday.
