970
FXCA62 TJSJ 170834
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
434 AM AST Mon Jun 17 2024

.SYNOPSIS...
Surface high pressure over the central and northeast Atlantic and an
elongated area of low pressure west of the region, will induce a weak
trough over the area to promote light east southeast winds through
Tuesday. High pressure will build north and east of region thereafter
promoting an increase in the easterly winds. The upper ridge will continue
to erode as a trough deepens west of the region. Moist and unstable
condtions will continue through mid week, with showers and isolated
thunderstorm likely each day, especially over the central interior
and northwestern quadrant of Puerto Rico. Fewer showers will be possible
around the U.S. Virgin Islands during the day. Dangerously hot and
humid conditions will persist with another round of slight to moderate
concentration of Saharan dust forecast to accompany and trail a tropical
wave expected to reach the area by Wednesday.

&&

.SHORT TERM...Today through Wednesday...

A variable weather pattern was observed during the early morning
hours today, with a few pockets of showers streaming across the
southeastern sections of Puerto Rico, Vieques, and the local waters.
According to estimates from the Doppler Radar, rainfall
accumulations were minimal across eastern sections of Puerto Rico.
Overnight temperatures were in the upper 70s to lower 80s across the
coastal areas and in the mid-60s to lower 70s across the interior.

For the rest of today into the short-term period, the islands are
forecast to observe a deteriorating weather pattern as an induced
surface trough from a deep upper-level trough moves just north of
the region. The instability provided by this feature and the
abundant moisture present in the area with PWAT above 2 inches, as
suggested by derived imagery from the GOES Satellite, indicate
another variable day in the morning, followed by an active afternoon
with high chances of thunderstorm activity across the interior
sections of the islands. As these surface features move and interact
with the broad surface high pressure in the Central Atlantic, the
islands will experience backing winds, which will become more
variable, especially in the afternoon. This factor will be
determinant in the movement of the showers, leaving the islands with
an elevated flood threat for today across most of the interior
sections; in the rest of the areas, the islands might experience
minor flooding with ponding of water in roadways and poor drainage
areas. In terms of temperatures, warmer minimum temperatures and the
southeasterly wind flow will provided another warm morning where
heat indices could reach 112 degrees.Given these conditions, for
today, yes again, an Excessive Heat Advisory is in effect for all
the northern, eastern, and western coastal areas of Puerto Rico,
including Culebra, Vieques, and the U.S. Virgin Islands.

By Tuesday, the surface winds will come again from the southeast,
leaving the islands under a variable pattern for the morning hours
until the next tropical wave shows up by late Tuesday into
Wednesday. Instability will be present due to the divergent side of
the upper-level trough just west of the region with the axis over
Hispaniola, resulting in enough moisture in 700-500 MB as suggested
by the RH in the model guidance and colder temperatures in the 500
MB. The Glvez-Davison Index (GDI) shows potential for daily
isolated to scattered thunderstorm activity. Although all the
variables favor a wet pattern, the NASA Goddard Earth Observing
System Model V5 shows a decent pulse of Saharan Air Dust across the
region early Wednesday, resulting in hazy skies and muggy conditions
across the region.

Given the expected conditions, residents should prepare for a
variable weather pattern for Tuesday morning, followed by afternoon
and evening showers across the eastern sections of Puerto Rico,
Culebra, Vieques, and the U.S. Virgin Islands in the early morning
hours of Wednesday when the tropical wave arrives in the CWA.

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

Moist and unstable weather conditions are expected to continue
through at least the early part of the period as a deepening
upper- level trough with the axis over Hispaniola west of the
region,will linger and provide good ventilation and a divergent
pattern aloft. This along with good tropical moisture convergence
produced by the prevailing and moderate east to southeast and a
passing tropical wave, will maintain good potential for shower and
thunderstorms development at least through Friday and moisture
trailing the wave will combine with the instability aloft and good
daytime heating to maintain moderate to high potential for
afternoon and early evening convection. Based on the most recent
guidance and Glvez-Davison Index (GDI)product, the potential for
isolated to scattered thunderstorm will continue through Friday.
Overnight and afternoon showers will be likely with a limited
flood threats across portions of the islands each day. Hazy skies
will continue at least through Thursday due to some lingering
Saharan Dust with improving conditions by Friday and into the
weekend.

Over the following weekend and through Monday, a broad surface
high pressure will again spread across the Central Atlantic and
Eastern Atlantic result in increasing east to southeast trade
winds and variable weather conditions. Under the expected low
level wind flow, plenty of surface moisture will continue to stream
across the islands and coastal waters, thus maintaining the potential
for passing showers overnight and afternoon convection each day.
This expected activity should be focused particularly across the
central interior and west sections of Puerto Rico,while the U.S.
Virgin Island can expect afternoon showers mainly on the west-end
and downwind of the islands with fewer shower activity elsewhere
from time to time.

A similar and slightly above normal temperature pattern is expected
to continue across the islands at least through the early part of
the long term. Model guidance remains persistent in maintaining overall
hot and humid conditions although the easterly are expected to increase
during the latter part of the period. Residents and visitors are
urged to stay informed of possible advisories or warnings due to
excessive heat conditions.

&&

.AVIATION...
(06Z TAFS)

VFR conditions will persist for all the morning hours across all the
TAF sites. By 17/17Z, brief MVFR conditions are forecast across TJSJ,
TJBQ, and TJPS due to t-storm activity developing across the interior
and the San Juan Metro area. This activity will affect VIS and ceilings
across the mountain area as well. Winds will become more light from
the E-SE, and more VRB after 17/22z.

&&

.MARINE...
Surface high pressure over the Atlantic and the proximity of an
induced trough across the region will promote light to moderate
east to southeast winds today through Tuesday. Passing showers
and isolated thunderstorms will continue to affect the coastal
waters and local passages resulting in localized hazardous marine
conditions especially over the offshore Atlantic and Caribbean
waters and between eastern Puerto Rico and the U.S. Virgin Islands
during the early morning hours and on the west coastal areas Turin
the afternoon hours. The easterly winds are forecast to increase
to moderate to locally fresh by late Wednesday and through the
rest of the work week.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for PRZ001-002-005-008-010-012-013.

     Excessive Heat Watch from Tuesday morning through Tuesday
     afternoon for PRZ001-002-005-008-010-012-013.

VI...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for VIZ001-002.

     Excessive Heat Watch from Tuesday morning through Tuesday
     afternoon for VIZ001-002.

AM...None.
&&

$$

SHORT TERM...LIS
LONG TERM....RAM
AVIATION...LIS