606
FXCA62 TJSJ 200802
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
402 AM AST Fri Sep 20 2024

.SYNOPSIS...
Light winds will persist through early next week. With light
winds, the afternoon showers and thunderstorms will linger,
increasing the potential for flooding and river rises, mostly for
the interior of Puerto Rico. The Virgin Islands and the coastal
areas in Puerto Rico will receive showers as well. Hot
temperatures will persist each day.

&&

.SHORT TERM...Today through Sunday...

Currently, radar and satellite imagery indicate calm and pleasant
weather across the forecast area, accompanied by light and variable
winds. Throughout the overnight period, some isolated showers have
moved over the local waters. Coastal and lower-elevation areas of
Puerto Rico are experiencing morning temperatures ranging from the
upper 70s to lower 80s, while higher elevations enjoy slightly
cooler conditions in the mid 60s to lower 70s. In the U.S. Virgin
Islands, temperatures are similarly in the upper 70s to lower 80s.

The unstable and wet weather pattern will persist in the short term.
The latest satellite-derived precipitable water values fluctuate
between 1.8 and 2.2 inches today, which is considered normal to
above normal. Conditions aloft will be favorable over the next few
days, maintaining instability for deep convection development, as a
TUTT (Tropical Upper Tropospheric Trough) lingers over the northeast
Caribbean. At the surface, light and variable winds will continue
throughout the short-term forecast.

For today, expect another day of showery activity during the morning
across the U.S. Virgin Islands and the eastern sectors of Puerto
Rico. This will be followed by enhanced shower activity due to
diurnal heating, leading to another round of showers and
thunderstorms, particularly across the Cordillera Central during the
early afternoon, spreading toward the coastal areas later in the
afternoon. Hazards include frequent lightning, gusty winds, and
urban and small stream flooding due to already saturated soils. On
Saturday and Sunday, shower activity is expected to be less intense
compared to today, but local effects and diurnal heating will still
promote afternoon convection, especially in the interior,
northwestern, and north-central Puerto Rico.

In addition, an elevated to significant heat risk will persist
through the weekend. Guidance indicates temperatures at 925 mb will
be two standard deviations above normal values, particularly on
Saturday. The combination of high temperatures and humidity could
create hazardous heat conditions. A Heat Advisory is in effect for
all coastal, urban, and low-elevation areas of Puerto Rico, as well
as for Vieques, Culebra, and the U.S. Virgin Islands. Residents and
visitors should monitor the forecast and take precautions to stay
hydrated by drinking plenty of water, wearing light and breathable
clothing, and avoiding prolonged sun exposure, especially during
peak heat hours.

In summary, moisture and favorable conditions aloft will lead to
additional showers and isolated thunderstorms today, with a broader
area likely experiencing limited to elevated flooding and lightning
risks. Local effects and diurnal heating will continue to promote
afternoon convection in some areas over the weekend. Hot conditions
are likely to persist in the coming days.

.LONG TERM...Monday through Thursday...

A deep-layered trough will continue to dig just north of the
Caribbean islands. This through will act to maintain a weak
steering flow, with speeds of 1 to 5 knots on Monday and Tuesday.
The through will gradually moves away by mid-week, with winds
gradually recovering speed, but only to around 10 knots. At the
surface, induced patches of moisture will move from time to time
through the period, although there are no particular day with a
great amount of low level moisture. This moisture will act to
generate some showers reaching the coastal areas of Puerto Rico
and the Virgin Islands each day. However, the strongest activity,
with thunderstorms, is expected each afternoon across the
Cordillera Central, with the activity then drifting toward the
coast. Since the winds will be so weak, it is difficult to
determine which area is going to be more affected, aside than the
interior that should receive the bulk of the activity each day.

As it has been the case in the past couple of weeks, above normal
temperatures will persist in the area, with the threat of
excessive heat each day. This heat will mainly impact those
without effective cooling or adequate hydration.

&&

.AVIATION...
(06Z TAFs)

Mainly VFR conditions are expected to prevail throughout the morning
forecast period, with visibility concerns likely at TJSJ and U.S.
Virgin Islands TAF sites. After 20/1700Z, additional activity is
anticipated to develop in the Cordillera Central, leading to
mountain obscuration that may affect TJPS. Winds will remain light
and variable, shifting to a southerly component at around 5 to 8
knots or less, becoming calm or light/variable after 20/2300Z.

&&

.MARINE...
A weak surface low pressure to the northeast of the region will
maintain weak and variable winds throughout early next week. Showers
and isolated thunderstorms will persist across the regional waters,
particularly off the western and southern coastal waters of Puerto
Rico each afternoon.


&&

.BEACH FORECAST...
The moderate rip current risk will persist for the northern coast
of Puerto Rico, Culebra, and some beaches in northwestern St. John
and eastern St. Croix.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon
     for PRZ001>003-005-007-008-010>013.

VI...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon
     for VIZ001-002.

AM...None.
&&

$$

SHORT TERM...YZR
LONG TERM....ERG