Eastern Caribbean: Potential for slow-moving low pressure forming quickly east of Windwards, rains may start early Thursday and potentially heavy rains continuing late Saturday to Sunday. “Models are late on this and are slowly catching up,” informed the meteorological department.
The department stated:
The models only recently showed slight development and mostly scattered rainfall, but the ICON was already showing more robust rainfall this morning. Tonight’s GFS and ICON both show the persistence of scattered areas of heavy rainfall, and the Euro has the surface trough moving very slowly even though weak. I don’t expect NHC to show much interest unless more model ensembles show development. But if one lives in Windwards, the individual should watch for excess rainfall potential.
Monday night: An upper-level low is north of the Leewards. It is embedded within an upper trough which extends south towards Venezuela, thus placing the islands on the favourable east side for enhancement of rainfall-producing clouds. The surface trough which was induced is now over the eastern Caribbean Sea, but lingering rain and showers remain over parts of the Lesser Antilles.
Less frequent showers are expected on most islands overnight. On Tuesday-Wednesday, a few moderate to heavy showers are possible as a tropical wave nears.
An interesting feature will help spark an area of spin within the ITCZ to the north of French Guiana and Suriname, just as the axis of a tropical wave passes from tonight through Wednesday. The feature I refer to is a South American cold surge coming from the south. It is already pushing ITCZ moisture north and NNE offshore of the Guianas, as seen on perceptible water products and low-level vorticity loops. It will help generate scattered heavy thunderstorms on Guianas also. See animation showing cold surge pushing moisture northwards across Guianas and also in western Venezuela to the east of the Andes mountains barrier: https://tropic.ssec.wisc.edu/real-time/mtpw2/product.php…
The models like GFS, ICON and Euro have started to forecast a low pressure forming within 24-48 hours. The ICON shows a developing low moving towards Barbados and Windwards early Thursday. The GFS showed slight weakening as it approached the islands and development right after passing, but a few ensemble tracks passed through the Barbados/Windwards. Even if no strong circulation forms, this system NEEDS to be watched whether it persists with thunderstorms or not since it will move VERY slowly towards and over the Windwards. The axis of the tropical wave will reach the islands Wednesday, but the potential low pressure or surface trough will slowly reach early Thursday and help produce rainfall thru overnight Saturday to Saturday. Flash flood risk will be moderate to high if this materializes.
The East Atlantic, tropical wave 90L, had some heavy thunderstorms early in the day but has weakened. NHC keeps a low chance of development. Models show it nearing the Leewards as a surface trough or weak low, but some ensemble tracks show some development. It passes late Sunday/early next week.
These features will maintain light winds for several days at the surface up to higher levels which means periods of slow-moving rainfall that lead to isolated flood and landslide events apart from the main Thursday-Sunday system of concern.