The South American Cold Surge, the GFS has been forecasting a cold surge rapidly pushing thru the continent northwards across the Amazon and pushing out to the Caribbean coasts and Guianas coast by 3rd November and 4th November. Ahead of the big push of cold air will be widespread scattered thunderstorms (some severe) arcing its way eventually into the Caribbean Sea and some across Guianas… by then they may be weaker but areas of convergence will be brought into the basin which will increase rainfall chances.
In the 1st image 2am, 1st Nov, has abnormally cold temperatures (-8C lower than normal! ) at 5000 ft and some strong winds starting from a deep upper trough east of the Andes/over Pampas in Argentina, SW Brazil and west Amazon basin…. 2nd image shows this cold air surging along the NW Amazon basin towards the Caribbean coasts and Guianas by 2am 3rd Nov with very strong 35-50kt (40-60mph) winds in spots east of the Andes… The Euro model also depicts the surge but is not as strong. The Canadian model has hints of it too in vorticity maps.
There are some recent GFS model runs which spin off 1 or 2 areas of spin at the edge of the surge once it reaches the Caribbean and SW Atlantic but that’s way in the 10+ days range. These surges can help spark tropical development but we more likely see enahnced rainfall.
The Andes Mountains stretch for the entire length of western South America and are very tall(often over 20K keet) so they act like a wall keeping the cold air hemmed in and easier to flow along. This type of event is not totally unusual(cold fronts reaching the hot, humid Amazon) but this is one of the intense ones.
Heavy rainfall fell on the Virgin Islands today. Some moderate to briefly heavy showers have also impacted Trinidad this evening.
Some heavy thunderstorms were to the west of the Lesser Antilles over water and the outflow from these brought cloudy to overcast skies. With the upper trough getting closer to the Lesser Antilles, weaker showers in the drier trade wind flow are being enhanced as they come towards the islands… bringing occasional moderate to heavy showers.
Overnight the ITCZ and weak surface trough will bring scattered moderate to heavy showers, periods of rain and a few thunderstorms to Trinidad and Tobago. Another surface trough entering Guyana will maintain similar weather on Thursday.
The ITCZ connects to the tropical wave of concern and as it passes the Guianas starting Thursday to Friday, some enhancement will take place with scattered thunderstorms in those areas then on Trinidad and Tobago and possibly southern Windwards, the upper trough will create conditions for more frequent showers, widespread rain, and scattered thunderstorms. Some of these heavy shower and rain periods push into the rest of the Windwards including St. Lucia to Dominica Friday to Saturday.
Trinidad and Tobago is on yellow alert. Recent periods of heavy rainfall since late last week leaves various areas on a heightened flood threat. Some flood risk will be over south Windwards with potential localized risk on rest of the Windwards to be determined closer to Friday/Saturday.
