Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 222009
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
409 PM AST Fri Mar 22 2024


.SYNOPSIS...

The weekend will be hot and breezy, but a cold front will bring
wetter conditions around mid-week, with cooler temperatures and
drier conditions after that. A northerly swell is expected to
arrive on Tuesday, deteriorating marine and beach conditions

&&

.SHORT TERM....SHORT TERM...Tonight through Sunday...

Today, a mixture of partly cloudy and sunny skies prevailed across
the islands. By the afternoon, showers started developing,
particularly across the interior, western, and southwestern
municipalities of Puerto Rico. The available moisture, diurnal
heating, and sea breeze variations contributed to the formation of
this activity. The heaviest accumulations were in the municipality
of Maricao, where a Flood Advisory was issued as the accumulations
reached around 2 inches. The maximum temperatures today ranged in
the mid to upper 80s along the coastal areas, while over the
higher terrains, they stayed in the 70s to low 80s.

As a low-pressure system continues to exit the southeastern coast
of the United States and interacts with the high-pressure system
over the Atlantic, expect the pressure gradient to tighten over
the northern Caribbean and increase wind speeds through Saturday
night. The available moisture content will decay at the mid-levels
and remain above normal at the low levels tonight. The surface
moisture will allow the development of some shower activity
tomorrow. The minimum temperature should remain in the 70s along
the coast and in the 60s across the mountainous areas.

By the end of the weekend, expect moisture levels to be near around
normal climatological levels for this time of the year. However,
as mentioned in previous discussions, Sunday`s weather conditions
will heavily depend on the track of the low-pressure system.
During the weekend, winds will become southerly. The latest model
guidance suggests the rainfall activity staying over the waters on
Sunday. Regardless, we can not rule out showers and possible
thunderstorm activity affecting northern Puerto Rico in the
afternoon, possibly shifting to windward coastal areas of the
islands during the evening hours. Stay tuned as this event
unfolds, possibly impacting the local islands through early next
week.

&&

.LONG TERM...Monday through Friday...
//from previous discussion//

The workweek should begin on a wet note, as a cold front
approaches the local islands from the west. The system appears to
preserve definitions all the way up into the mid-levels of the
atmosphere, so conditions should be favorable for periods of heavy
rain and isolated thunderstorms on Monday and Tuesday. First, on
Monday, the areas that should begin to receive the greatest
amounts of rain will be the north and west of Puerto Rico, but
the moisture field will eventually move into the southern half of
Puerto Rico, reaching the Virgin Islands late Monday or early
Tuesday. The global models agree on this frontal passage early in
the week, although the ECMWF is a little faster, ending most of
the rain by late Monday.

Moving into the middle of the week, columnar moisture decreases,
with precipitable water values likely dropping below 1.0 inch, and
a trade wind cap inversion developing around 850 mb. Therefore,
the potential for showers will decrease considerably, and will be
limited to small patches occasionally reaching the islands. The
wind flow will remain from the northwest for most of the week, and
fairly light. Temperatures will be a little cooler too during this
period, but with highs still reaching the mid-80s.

&&

.AVIATION...
(18Z TAFS)

Mainly VFR conditions expected across the local terminals. Winds
will continue from the E/ENE at 15-20 kt with higher gusts and sea
breeze variations. SHRA/+SHRA will dissipate along the Cordillera
Central and western sections by the evening hours, leaving mainly
clear skies. Trade wind showers will arrive from time to time
overnight, and could affect TJSJ/TISX/TIST after 23/00z, resulting
in VCSH. Winds will become calm to light and vrb after 22/23z.

&&

.MARINE...
A surface high pressure is building over the Western Atlantic and
will promote moderate to locally fresh easterly winds tonight. This
surface high pressure will spread into the central and eastern
Atlantic, enhancing the easterlies and promoting choppy seas through
late Saturday. Another surface low pressure and associated frontal
boundary exiting the US Eastern Seaboard and drifting eastward will
approach the region around Sunday, promoting light southerly winds
early next week. A long-Dominant period northerly swell will arrive
around Tuesday

&&

.BEACH FORECAST...
Breezy conditions are expected in the beach areas, especially in
the afternoon hours. The risk of rip currents is now moderate for
the north-facing beaches in Puerto Rico, Culebra, and the U.S.
Virgin Islands.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM...MMC/ICP
LONG TERM....ERG
AVIATION...CAM
MARINE...MMC
BEACH FORECAST...MMC
PUBLIC DESK...RC


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