Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
1017 AM EST Thu Mar 06 2025

Weekly Discussion for Puerto Rico and the USVI 06 March 2025

A relatively variable weather pattern is expected across PR/USVI
over the next several days. This is due to some synoptic features
that will be having an impact in the overall moisture, wind
direction, and instability. In general, today and Friday are
expected to be the days with best chances of rainfall across the
local islands, with a decreasing trend of significant rainfall
each day this weekend into early next week.

In the upper levels, there is a trough to the NNE of PR/USVI that
is also causing a deepening in pressures and inducing troughs in
the mid and lower levels. This upper trough will move east through
today, then a weak upper trough will move through the Caribbean
Friday, reaching the eastern Caribbean by late Saturday. By the
late weekend, an upper high pressure across the western Caribbean
will extend into the eastern Caribbean by Monday. That said, an
upper diffluent pattern may be observed across the eastern
Caribbean by Tuesday, but the impact of that diffluence may be
limited, due to some stability in the mid levels and drier than
normal moisture over the area during that time.

There is a mid-level low across the western tropical Atlantic, and
a mid-level high pressure that will develop over extreme western
Caribbean and extend into eastern Caribbean starting on Friday.
This mid-level high pressure will move east through the weekend,
and will be centered over PR/USVI by Monday night. This mid-level
high pressure will provide some stability to the local area, and
will contribute to the development of a trade wind inversion from
the weekend onward, causing a decreasing trend of significant
rainfall over the local islands from the weekend into the
beginning of the upcoming workweek.

There are several significant features in the lower levels, which
will have a significant impact on the amount and location of the
rainfall expected, especially today and Friday. At the surface,
there is a high pressure in the central Atlantic. There is also a
SFC trough across the western tropical Atlantic, associated with
the mid-level low and the upper trough over the area. This SFC
trough extends down to the northeast Caribbean, which is causing
moisture convergence across the local islands, and is expected to
do so today and Friday, and therefore increasing the chances of
rainfall over the area. Elsewhere across the Atlantic basin, there
is a cold front that will pass just north of PR/USVI by Friday
night, moving away on Saturday. At the same time, a SFC high
pressure will move east into the western tropical Atlantic. This
high pressure will meander over the western tropical Atlantic from
the weekend into Monday. By Tuesday, a SFC low will exit the east
coast of the USA and enter the western Atlantic, reaching the
central Atlantic by late Wednesday.

This SFC pattern will cause changes in the wind speed and
direction over the local islands for the next several days. Winds
will be from the S-SSE today, then light and variable on Friday as
there may be a COL over the area. Winds will then shift to an ENE
direction by Saturday into Sunday, then easterly on Monday,
shifting southeast by Tuesday and Wednesday. These wind changes
will play a role on the location of the sea breeze convergence
over PR, having an impact on where the afternoon convection will
occur. The available moisture will be highest today and to a
lesser degree on Friday, due to the aforementioned low-level
trough. The available moisture will decrease gradually over the
local area with each passing day. By Saturday, and for several
days thereafter, the moisture at 700mb and into the mid levels
will be below normal, suggesting that the available moisture will
be limited to the lower levels. For that reason, it is expected
that the convection that does develop over PR in the afternoons
will be relatively shallow from the weekend onward, also having to
consider the general stability in the mid levels expected during
that time.

In terms of rainfall pattern over PR/USVI, showers and
thunderstorms can be expected today and Friday over the local
islands, with the best chance of afternoon convection favoring
portions of central to northern PR today, then central to western
PR on Friday.  That being said, there is the potential for good
rainfall accumulations across the higher elevations of eastern PR
as well. At least scattered showers are expected today over
Vieques, Culebra, and the USVI, while locally numerous showers are
possible tomorrow over the islands, with a drying trend expected
thereafter.

Alamo...WPC (USA)