880
FXCA62 TJSJ 140857
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
457 AM AST Tue May 14 2024

.SYNOPSIS...

Stable weather patterns will prevail for the next several days in
the morning hours, followed by afternoon convection each day
across the interior sections of the island. Clear to partly cloudy
skies in the morning will allow warmer temperatures, increasing
the heat indices across the northern sections. Although slightly
warmer, heat indices will fluctuate between 102 and 107 degrees
Fahrenheit. Therefore, residents should stay hydrated and tune for
further updates. A similar pattern is forecasted until Thursday
when surface winds will increase from the southeast. Instability
will be a defining factor for the upcoming workweek, increasing
the potential for shower development.

&&

.SHORT TERM...Today through Thursday...

Skies were mostly clear to partly cloudy overnight with isolated to
scattered passing showers noted over the offshore coastal waters,
and limited to no shower activity noted over land areas. Overnight
low temperatures were in the upper 70s to low 80s along the coastal
areas and near mid 60s to low 70s in higher elevations and valleys.
Surface winds were calm to light and variable.

Overall warm and mostly fair weather conditions are expected today
for much of Puerto Rico and the adjacent islands including the U.S.
Virgin Islands.  Under a fairly light east southeast wind flow and
mostly sunny skies, daytime highs will reach the upper 80s to low
90s along the coastal areas with maximum heat indices to range
between 100 and 107 degrees particularly along the northwest to
north coastal areas and in urban areas of Puerto Rico including
Vieques, Culebra and portions of the U.S. Virgin Islands. Afternoon
showers and possibly an isolated thunderstorm or two cannot be ruled
out over portions of the central and west sections of Puerto Rico
with the chance of locally heavy rains, which may lead to ponding of
water on roads and in poorly drained areas and with the possibility
of minor urban and small stream flooding in isolated spots. Fewer
afternoon shower activity is expected elsewhere and only on the west-
end and downwind of the U.S. Virgin Islands.

For the rest of the short-term period, a somewhat drier trend and
more seasonal weather pattern is forecast as winds slightly increase
and become more east to northeast by Wednesday and Thursday. A mid-
to upper level high-pressure system will continue spread eastwards
across the region from the west and southwest Atlantic, while a
surface high pressure will build across the west Atlantic.
Consequently this will increase the trade wind cap inversion while
eroding low level moisture. Recent analysis and NASA aerosol optical
thickness continued to suggest only light concentrations of Saharan
dust to persist at least through Wednesday. Latest model guidance as
well as satellite derived analyses all suggest overall PWAT values
to continue to diminish and range between 1.4 and 1.7 inches for
today, then slightly increase to between 1.5-1.8 inches for the rest
of the period as winds become more easterly and slightly increase.

That said, although the overall synoptic conditions are forecast to
be less conducive for significant convective development, shower
development and possibly an isolated thunderstorm will remain
possible each afternoon especially over parts of the central
interior and west sections of Puerto Rico locally steered by the
east to northeast low level wind flow. Warm conditions and slightly
above normal temperatures are expected to continue for the next few
days with daytime temperatures peaking in the upper 80s to low 90s
along the coastal and urban areas. Residents and visitors to the
islands are urged to stay hydrated and limit direct sun exposure
when possible.

.LONG TERM...Friday through Tuesday...

The long-term forecast remains on track. A broad surface high-
pressure extending from the north-central Atlantic into the
Caribbean will maintain the east-southeasterly wind flow across
the region. During the first section of the period, tropical
moisture dragged by the surface winds and some instability (lower
250 MB height) will trigger afternoon convection each day. An
induced surface trough will weaken the pressure gradient at the
north, resulting in southeasterly light to moderate winds. Surface
winds from the southeast will drive most of the showers across
Puerto Rico`s interior and northwestern quadrant. The most
vigorous shower activity and the light steering flow would result
in enough rainfall accumulation to cause a minor flooding threat.
By Monday into Tuesday, mid to upper-level conditions change, as a
trough results in instability aloft and colder temperatures at the
500 MB level. According to the Galvez-Davison Index (GFS output),
there is a high probability of experiment-isolated thunderstorms,
especially in the afternoon hours each day. Given the expected
conditions, the flood threat is forecast for the last part of the
long-term.

&&

.AVIATION...(06Z TAFS)

VFR conds through the fcst prd. Isold-SCT SHRA mainly over the
regional waters and en route to the islands. Mstly SCT lyrs nr
FL028...FL050...FL250. Aftn SHRA/Psbl isold TSRA ovr ctrl and west
interior sections of PR fm 14/18-22Z with VCSH psbl at TJBQ/TJSJ til
23Z. Calm to lgt/vrb wnds will become mainly fm E around 10-13 kts
with ocnly hir gusts and sea breeze variations aft 14/14Z.

&&

.MARINE...

A surface high-pressure system over the western Atlantic will
continue to promote light to moderate easterly winds across the
region. These conditions will lead to tranquil marine conditions
for all the local waters, with seas up to 5 feet in the offshore
waters and up to 4 feet in the coastal waters. Winds will continue
from the east at 15 knots or less for the next several days,
becoming more from the southeast due to a surface high pressure in
the central Atlantic.Recent forecasts show tranquil marine
conditions with seas up to 4 feet and periods of 8 seconds.
Therefore, there is a low rip current risk for the next several
days across all the exposed coastal areas.

&&

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

$$

SHORT TERM & AVIATION...RAM
LONG TERM & MARINE....LIS