Tropical Discussion - International Desks
NWS Weather Prediction Center College Park MD
943 AM EST Thu Feb 20 2025

Weekly Discussion for Puerto Rico and the USVI 20 February 2025

Taking a look at the upper levels and the large scale, on
Thursday, model guidance is suggesting the Madden-Julian
Oscillation (MJO) divergent phase is located over region 8, which
suggests it is entering Central America and nearing the Caribbean
Basin. However, the propagation and location of the divergent
phase has presented a more disorganized pattern over the past
several days and model guidance is suggesting that this will
continue this week and into the following work week. Although
disorganized, expect divergent conditions in the upper levels to
favor deep convection if the conditions in the other levels of the
atmosphere are favorable over the next week.

In the short range, on Thursday and Friday, the upper level
subtropical ridge is centered over north Colombia and extends over
the Caribbean Basin, while a mid-level ridge extends of the
northern Caribbean from the Central Atlantic, favoring a weak
trade wind inversion and the presence of dry air over Puerto
Rico/VI and the north Caribbean. In the lower levels, moist plumes
in the trade winds are propagating westward over the Puerto Rico
and the Leeward Islands, which could bring shallow convection with
them. Models are suggesting that available moisture can increase
from Thursday into Friday in the region but the mid to upper level
conditions may not assist with heavy precipitation. Expect daily
maxima to remain below 0.5 inches on Thursday and Friday.

From Friday evening into Saturday, a cold front is propagating
southward over the Bahamas/Turks and Caicos and developing a
prefrontal shear line north of Puerto Rico by early Saturday. In
addition, the development of a prefrontal trough is expected over
the Leeward Islands on Friday and Saturday, expected to move
westward to Puerto Rico from Saturday afternoon into early Sunday
evening. In the mid to upper levels on Saturday afternoon, a
shortwave trough is expected to propagate over Puerto Rico, which
could provide assistance with deeper convection as the prefrontal
trough passes the islands. Precipitable water values could reach
over 1.6 inches by Saturday evening into Sunday morning.
Precipitation totals with this event could reach 1 inch or more
locally in East and Northeast Puerto Rico, and potentially into
Vieques and Culebra by Sunday morning. 

Looking further into the next work week, in the upper levels, the
subtropical ridge is expected to weaken in the beginning of the
week and then strengthen by midweek while a deep upper level
trough is expected to propagate southward from South United States
into the west Caribbean by Tuesday into Wednesday. A weak trade
wind inversion and dry air are expected over the first part of the
week. In the lower levels, weaker moist plumes are expected to
propagate in the Easterly Trade Winds and reach Puerto Rico/VI but
the effects are expected to remain minimal in terms of rainfall
totals. By the middle of next week another frontal boundary is
expected over the Atlantic Basin and into The Bahamas/Turks and
Caicos, that could favor a shift in wind direction in the lower
levels from East to Northeast over the region. The confidence
decreases for the later part of the forecast period, however,
model guidance is in agreement that available moisture could
increase over portions of the north Caribbean by the middle of
next week. In terms of precipitation, expect seasonal diurnal
showers to dominate in the beginning of the week, while chances of
increased values of precipitation in East and south Puerto Rico
increases in the middle of the week. Daily precipitation totals
are generally expected to remain below 0.5 inches over the region.

Castellanos...WPC(USA)