263
FXCA62 TJSJ 152135
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
535 PM AST Wed May 15 2024

SYNOPSIS...

A typical weather pattern is forecasted for the next several days,
featuring afternoon showers across the interior and western sections
of the island. An increase in shower activity is expected for the
upcoming workweek due to the arrival of abundant tropical moisture
and instability facilitated by a mid to upper-level trough. Residents
and visitors are urged to stay tuned for further updates for the
upcoming workweek.

&&

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

Similar to the past few days, calm conditions prevailed during the
morning hours followed by convection in the early afternoon hours
across the interior and southwest quadrant of Puerto Rico. According
to radar estimates, at the moment between 1 to 1.5 inches of rain
have fallen in municipalities such as Aasco, San German, Juana
Diaz, and Adjuntas. The rest of the areas have seen half-inch or
less to zero rain. Not many changes are expected for tonight`s
period, showers should continue to fade after sunset allowing
generally calm weather conditions with easterly winds around 5 to
10 mph.

The short-term forecast remains on track. According to the latest
models, a mid to upper-level high-pressure system will continue to
spread eastward across the region from the western to southwestern
Atlantic, while another surface high pressure moves in the western
and central Atlantic. Moisture levels should remain within the
normal range, between 1.5 and 1.8 inches of precipitable water
tomorrow through Friday. Winds become more easterly to southeastern
as an easterly disturbance approaches the forecast area along
with an upper trough crossing the western Atlantic next Friday.
This could result in more favorable conditions for the development
of rain in the afternoon hours and possible isolated thunderstorms.
Due to the change in wind flow, showers could concentrate in the
northeast quadrant and interior of Puerto Rico during the afternoon
hours. In addition, that will favor the warm temperatures to continue,
with daytime temperatures peaking in the upper 80s to low 90s along
the coastal and urban areas and heat indices may range between
100-107 degrees Fahrenheit during the afternoon hours. Residents
and visitors to the islands are encouraged to stay hydrated and
limit direct sun exposure when possible.

&&

.LONG TERM...Saturday through Wednesday...
.PREV DISCUSSION... /issued 431 AM AST Wed May 15 2024/

A surface high pressure system extending from the central
Atlantic will maintain southeasterly winds across the region in
the initial phase of the long-term forecast. These winds will
carry patches of tropical moisture to the local islands, enhancing
the likelihood of shower formation, particularly in the
afternoon. Most showers are anticipated to develop across the
interior, the northwestern quadrant, and the San Juan metro area.
Some sections of the islands may experience clear skies in the
mornings, coupled with available moisture, which could elevate
heat indices, posing a limited to elevated heat threat for the
northern coastal area of Puerto Rico.

Instability is expected to increase by late Sunday and persist
throughout the forecast period as a mid to upper-level trough
moves from the western Atlantic. According to guidance from global
models such as the GFS and ECMWF, the strongest and most
favorable side of the TUTT (Tropical Upper Tropospheric Trough)
and its associated jet stream will cover the local islands from
Monday through Wednesday. With aloft instability and colder
temperatures at mid-levels, abundant tropical moisture will be
present at the surface, with precipitable water (PWAT) values
exceeding climatological norms by over 2 inches. Consequently, a
wet period is forecasted for all the islands, characterized by
morning shower activity followed by widespread showers and
thunderstorms in the afternoon. Residents and visitors should
anticipate periods of heavy showers and an increased risk of
flooding from Tuesday through Wednesday.

&&

.AVIATION...
(18Z TAFS)

Mainly VFR conditions expected to prevail through the forecast
period. SHRA are expected to linger across the Cordillera Central
through 22Z, with mountain obscuration possible. VCTS are possible
for TJPS during this period as well, and brief periods of reduced
VIS and low ceilings are possible. VCSH are also expected for the
USVI terminals after 22Z. Winds will be from the E below 10 knots
tonight, increasing to 10-12 kts after 16/14Z.

&&

.MARINE...
A surface high pressure extending from the western Atlantic into
the Central Atlantic will continue to promote light to moderate
easterly winds across the region. With this pattern, seas will
remain up to 4 feet across all the local waters and passages.
These conditions will prevail across the local waters during the
period. Similar tranquil marine conditions are expected for the
coastal areas, where the risk for rip currents will remain low
for the next five days or so.

&&

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

&&

$$

SHORT TERM...YZR/CAM
AVIATION...ERG/CAM
LONG TERM....LIS
PUBLIC...RC