Graphical Hazardous Weather Outlook


Lightning THREAT





FXCA62 TJSJ 262115

Area Forecast Discussion
National Weather Service San Juan PR
515 PM AST Mon Feb 26 2024


Issued at 500 PM AST Mon Feb 26 2024

Merging cold fronts over the area will provide ample moisture and
some convergence in northeasterly flow to hold clouds and showers
over the area until Wednesday. A long wave trough with colder air
aloft will increase instability and the possibility of thunderstorms
tonight and Tuesday. Then, a gradual improvement in weather conditions
is anticipated for the latter part of the week despite the development
of quick passing showers.


.SHORT TERM...Tonight through Wednesday...

The skies remained cloudy today, with near to below-normal
temperatures across most islands due to a frontal boundary and
associated pre- frontal trough. VITEMA officials reported minor
flooding across St. Croix early this afternoon, where a flood
advisory was issued.

Unstable and wet weather conditions will continue across the islands
in the short term period. GOES-E Total Precipitable Water (TPW)
imagery showed above-normal moisture; those values will last over
Puerto Rico and the U.S. Virgin Islands through at least early
Wednesday. The frontal boundary will linger over the northeast
Caribbean due to the interaction between two surface high pressures,
one moving northeastward across the western Atlantic and another
across the far northeast Atlantic. In the meantime, the mid to
upper-level trough will keep the instability across the region,
especially tomorrow, when its axis will approach the forecast area
from the west. Additionally, latest model guidance suggests mid-
level temperatures will decrease to near -8C and -10C this evening
into Tuesday and the presence of some saharan dust near the region.
Given this configuration, the potential for the development of
isolated thunderstorms increases tonight and tomorrow (Tuesday),
especially across northeastern PR, the interior, and southwest PR.
We encourage residents and visitors to remain weather-aware and
exercise caution on the the roads, as localized ponding of water
on roads and poorly drained areas remains possible with the
heaviest rainfall activity.

The chances of significant rainfall are expected to decrease
beginning Wednesday afternoon as a strong high-pressure ridge
starts building aloft, diminishing cloud cover and shower
activity. A surface high-pressure ridge will also develop and move
into the southwest Atlantic and build across the region, resulting
in northeasterly winds and the return of more stable weather


.LONG TERM...Thursday through Sunday...
/from previous discussion/

High pressure at the surface in the western Atlantic will be
refreshed later in the week with another high out of the eastern
United States. A persistent inverted trough that wanders between
55 and 45 degrees west longitude in the sub-tropical Atlantic will
also help to maintain northeasterly flow across Puerto Rico and
the U.S. Virgin Islands through the long term period. This will
bring cool and fairly moist air out of the central Atlantic in the
lower levels. Although mid levels will be dry, the persistent
winds of 10 to 20 knots and the abundance of low level moisture
will produce bands of showers that will bring night and early
morning showers to the U.S. Virgin Islands and the north and
northeast coastal sections of Puerto Rico and afternoon showers to
the southwestern and interior portions of Puerto Rico. Amounts
are not expected to be particularly heavy, but will help to
alleviate the drier periods of the previous week. Because of the
uniformity of the air flow during the period out of the cooler
central Atlantic temperatures will be in a slight cooling trend
overall, but will be warmest on the south coast.

At upper levels on Thursday and Friday, the atmosphere will
recover from the cold it caught during the passage of a long wave
trough Tuesday and Wednesday. We will begin to feel the effects
of a weaker short wave trough Saturday and Sunday.


(18Z TAFS)
Issued at 500 PM AST Mon Feb 26 2024

Unsettled weather conds will prevail across the region due to a
frontal boundary and an approaching jet stream, enhancing the
potential for TSRA development near the local flying area each
day. Therefore, TSRA/SHRA may impact local terminals (JSJ/JPS/IST/ISX)
during the afternoon and late tonight (27/02-08z) near JSJ/IST/ISX.
Winds will prevail from the ENE-NNE at 5 to 15 kt and gusty with
sea breeze variations. Winds will become calm to light and VRB aft
26/23z, returning from the ENE tomorrow aft 27/12z.


Issued at 500 PM AST Mon Feb 26 2024

Seas will be generally gentle with moderate short period wave
action due to persistent northeast flow. A weak pulse of swell
from a low moving northeast out of the western Atlantic reached
the area today, but more significant wave action will be generated
by local winds Friday through Sunday when Small Craft Advisories
will likely be necessary in the local outer Atlantic waters.





NWS SJU Office Area Forecast Discussion



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