914
FXCA62 TJSJ 042007
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
407 PM AST Wed Dec 4 2024

.SYNOPSIS...
Passing showers will continue to move across the region,
especially along eastern Puerto Rico and the Virgin Islands in the
morning hours, and in the west in the afternoon hours.
Temperatures will remain slightly above normal, especially in
urban and coastal areas. The risk of rip currents will be moderate
through early in the weekend, and could become high by early next
week.

&&

.SHORT TERM...Tonight through Friday...

Sunny to partly cloudy skies prevailed across the islands today. The
Doppler radar estimated near half an inch of rain over St. John and
close to an inch across portions of northeastern, central, and
western Puerto Rico. High temperatures were from the mid and upper
80s across the northern sections of the islands, and from the upper
80s to low 90s across the southern coastal areas. The wind was from
the east to southeast between 10 and 15 mph with sea breeze
variations and higher gusts along coastal areas. Increasing trades
and a more east to northeasterly component in the winds are
expected from tonight through Thursday, with a few trade wind
perturbations shifting briefly the winds from the ESE.

A building mid-to upper-level ridge over the northeastern Caribbean
should promote warmer than normal 500 mb temperatures and drier air
aloft through the short term period. However, a weak upper-level
trough rounding the top of the ridge may cause some brief
enhancement of a trade wind perturbation on Thursday night/early
Friday morning. Therefore, passing showers should increase during
this period across the USVI and eastern PR, with possible isolated
thunderstorms developing over portions of the local waters.
Otherwise, relative fair weather conditions should prevail during
the rest of the forecast period.

Normal to above normal temperatures are expected to prevail each
day, with highs in the upper 80s along the northern coastal areas,
and in the low 90s along the southern coast of PR, and St. Croix.

.LONG TERM...Saturday through Wednesday.../from prev discussion/...

A mid-high pressure system over the Caribbean will create a
relatively stable weather pattern during the weekend. This
pattern will dry out the mid-levels of the atmosphere and promote
subsidence, which will confine available moisture to around or
below 850 MB. As the mid-level high pressure moves into the
western Caribbean, a TUTT low is expected to develop from the
northeast and reach the US Caribbean by late Monday, extending
into mid-next week. A jet stream will also approach the region as
early as Monday morning. As the TUTT-low remains near the Lesser
Antilles, it will induce a surface low that may move closer to the
islands by the second part of the following workweek.

This TUTT low will affect the islands from the northeast, causing
wind perturbations that will be carried across Puerto Rico and
the U.S. Virgin Islands by the trade winds, mainly from Monday to
Wednesday. Once again, global models show discrepancies in the
intensity and position of the TUTT low, ultimately influencing the
weather patterns that develop across the local islands. As a
result, there is significant uncertainty regarding the amount of
precipitation we might experience in the long-term forecast.

Moisture over the islands will be influenced by a cold front
moving across the western Atlantic during the weekend, remnants
of an old boundary, and a high-pressure system over the North
Atlantic. These frontal boundaries could approach the islands by
Tuesday. Still, easterly winds will bring plenty of low-level
moisture to the northeast Caribbean, leading to a typical tropical
winter rain pattern and cooling local temperatures.

Expect a mix of sunshine/clear skies and clouds daily, with
moisture primarily in the mornings and evenings. Orographic
effects, diurnal heating, and sea breezes will drive afternoon
convection in western Puerto Rico. Rain frequency and intensity
will likely increase next week as the upper-level ridge weakens
and trade wind disturbances arrive.

The return of the trade winds may cause a cooling trend in
temperatures, although this is still connected to sea surface
temperatures, which are currently one to two degrees Celsius above
normal for this time of year.

&&

.AVIATION...
(18Z TAFS)

SHRA/TSRA in and around TJBQ should end around 22z. VFR expected to
prevail across all terminals through the fcst period. Trade wind
SHRA could move briefly overnight across the USVI/Eastern PR
terminals. The 04/12z TJSJ sounding indicated E-ESE winds up to 18
kt blo FL070.

&&

.MARINE...
A surface high pressure over the central Atlantic and a frontal
system extending across the western Atlantic will promote a moderate
to locally fresh east to east-southeasterly wind flow through
tomorrow. A prefrontal trough will promote additional showers and
thunderstorms across the surrounding waters tonight and tomorrow.
Winds will then return from the east-northeast as the frontal
boundary lingers north of the northeastern Caribbean from Friday
onward. A northerly to northwesterly swell could move across the
Atlantic Offshore waters by the weekend.

&&

.BEACH FORECAST...
A small northerly swell continues to invade the local waters.
This, along with the winds, is promoting a moderate rip current.
The risk will increase to high by late Sunday or Monday as a
potential larger swell arrives.

&&

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

$$

SHORT TERM...ERG
LONG TERM....MNG