Area Forecast Discussion
Issued by NWS San Juan, PR

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136
FXCA62 TJSJ 292000
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
400 PM AST Wed May 29 2024

.SYNOPSIS...

Moisture content is expected to remain normal to above normal,
enhancing the potential for afternoon convective activity across
northwest Puerto Rico through at least Thursday. A tropical wave
is expected to approach the region by Thursday, however, the bulk
of moisture should remain over the Caribbean waters. Drier air is
expected to filter into the area by the end of the workweek,
accompanied by Saharan dust particles.

&&

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

During the morning hours, light showers filtered over the eastern
half of Puerto Rico, leaving less than an inch of rain. The
typical afternoon convection developed over the western interior
and northwestern sections of Puerto Rico, where the concentrations
ranged above an inch of rain. Nonetheless, the intensity of the
rainfall and thunderstorm activity was not as strong as in
previous days. Overall, seasonal weather conditions prevailed with
the east-southeasterly wind flow. Temperature-wise, they remained
in the upper 80s to low 90s along the coastal and urban areas,
while over the higher elevations, they stayed in the upper 70s to
low 80s. Heat indices today stayed below 111 degrees Fahrenheit
across Puerto Rico and the U.S. Virgin Islands, staying within the
thresholds for Heat Advisory criteria.

Tonight, expect variably cloudy skies to prevail across Puerto Rico
and the U.S. Virgin Islands as patches of moisture move across
the area from time to time. The overnight temperatures should stay
in the upper 60s to low 70s across higher elevations and in the
80s along the coastal areas. Wind-wise, they should stay generally
light and variable, influenced by land breezes.

The latest model guidance continues to suggest the precipitable water
content staying around normal to above normal levels through
Thursday when a tropical wave moves across the Caribbean waters.
The increase in moisture associated with the proximity of the wave
will aid in the development of showers and thunderstorms across
the region. As usual, after the passage of a tropical wave, a mass
of drier air with suspended Saharan dust will filter across the
region on Friday. Nonetheless, the local effects combined with the
available low-level moisture will trigger afternoon showers and
isolated thunderstorms once again, particularly across western
Puerto Rico. As mentioned in previous discussions, the warm to hot
temperatures will continue through the short-term period under
moist east to southeasterly winds. Heat indices are expected to
range from 104 to 112 degrees Fahrenheit, mainly along the lower
elevations of western and northern Puerto Rico and St. Croix.

&&

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

A surface high pressure in the central Atlantic will promote south
southeasterly winds through much of the long-term-period. Plenty of
abundant tropical moisture moving into the local area will help
to maintain a wet and unstable pattern across the islands. The
latest Precipitable Water Content analysis (PWAT) suggest values
of 2.3 to 2.5 inches between Sunday through Monday. This is in
response of the development of a surface trough west of the region
that will enhance the shower and thunderstorm potential across
Puerto Rico and the U.S. Virgin Islands. Sufficient moisture in
combination with daytime heating and local effects, will lead to
convective activity across the central interior and northwestern
portions of Puerto Rico during the afternoon hours. Therefore,
there is a limited to elevated risk of isolated flash flooding,
urban and small stream flooding, river rises, and mudslides. By
Tuesday into Wednesday as the surface trough lingers north of the
area, moisture from the Caribbean waters will continue to be
lifted and moved over the islands. Winds are expected to veer from
the south by Tuesday in response to the combination of the
surface trough and a approaching tropical wave. With this scenario
the potential for moderate to heavy rainfall and isolated
thunderstorms remains high. Despite the anticipated weather
scenario, warmer to hot temperatures are expected each day.
Daytime temperatures are expected to reach the upper 80s to low
90s. Meanwhile, overnight temperatures will remain in the upper
70s to low 80s along the coastal and urban areas of the islands.
Heat indices may reach the mid to upper 100s during the period,
especially during the mid-morning to early afternoon hours.

&&

.AVIATION...

(18z TAFs)

Aftn convection will remain psbl mainly across the ctrl Mtn range of
PR and downwind from the USVI til 29/23Z. SHRA/VCTS with ocnly gusts
btwn 15-25kt psbl at TJBQ and vcty til 29/23z. SFC wnds mainly fm E
at 15 kt or less with sea breeze variations, bcmg calm to lgt/vrb
aft 29/23Z. Expect E winds at 10-15 kt with sea breeze variations
and ocnly hir gusts aft 30/14Z.

&&

.MARINE...

A moderate east to southeast wind flow will prevail across the region
over the next few days. The next tropical wave will move into the
Eastern Caribbean later tonight, moving far to the south of Puerto
Rico and the U.S. Virgin Islands between early Thursday and early
Friday.

&&

.BEACH FORECAST...

There is a moderate risk of rip currents across the northwestern
beaches of Puerto Rico, and the beaches of St. Croix. Elsewhere,
there is a low risk. Moderate to heavy showers and isolated
thunderstorms are possible each afternoon mainly across the
northwestern waters of Puerto Rico.

&&

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

$$

SHORT TERM...MMC/RAM
LONG TERM....GRS
AVIATION...RAM
PUBLIC DESK...RVT