483
FXCA62 TJSJ 312045
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
445 PM AST Fri May 31 2024

.SYNOPSIS...

Short-term concerns include continued heat through the weekend,
daily afternoon showers and thunderstorms mainly across the interior
and western Puerto Rico, and the arrival of Saharan dust, contributing
to hazy skies and elevated to moderate heat risk. Wet and unstable
conditions are expected early next week due to an approaching
tropical wave.

&&

.SHORT TERM...Tonight through Sunday...

Generally calm conditions prevailed during the morning hours with
only a few spotty showers in the Caribbean Sea and eastern sectors
of Puerto Rico. As it was expected, thunderstorm activity
developed by the early afternoon hours across the northwestern
quadrant of Puerto Rico leaving around 1 to 1.5 inches of rain.
Weather conditions are expected to improve after sunset due to
diminishing surface heating. A Flood Advisory was issued for
Aguadilla, Isabela, and Quebradillas due to that rain activity.
Temperature-wise, it was another hot day as southerly winds
persisted, and a new record daily maximum temperature was set in
San Juan Airport with 94F, breaking the old record of 93F of
2006.

Under an east-southeast steering wind flow, a similar pattern is
expected over the weekend with passing showers moving in over
windward coastal areas of Puerto Rico and Caribbean Waters during
the late night and morning hours, with convective activity
clustering over the northwestern quadrant of Puerto Rico each
afternoon and precipitable water values running around 1.70 to
2.00 inches. Any heavy rain could lead to some urban and small
stream flooding. Due to an approaching tropical wave; now located
at 50W, the moisture content will increase within the 75th and
90th percentiles from late Saturday onwards, higher than the
climatological norm. For the remainder of the weekend, the GEOS-5
model continues to suggest Saharan dust particles suspended over
the islands leading to hazy skies across the northeastern
Caribbean and could slightly suppress rain development in some
areas.

The 925 mb temperatures will remain well above normal for this
time of year through the weekend. High temperatures combined with
above-normal moisture could promote hazardous heat conditions,
particularly across coastal and urban areas. Therefore, it is very
likely that Heat Advisories and possibly Excessive Heat Warnings
may continue to be needed each day over the weekend. Residents and
visitors are encouraged to limit outdoor activities, drink plenty
of water, and wear lightweight clothing.

&&

.LONG TERM...Monday through Friday...
.PREV DISCUSSION... /issued 501 AM AST Fri May 31 2024/

The lingering moisture from a departing tropical wave is set to
continue promoting shower and thunderstorm activity across the
region on Monday, with some thunderstorms potentially being strong
over western PR. Following this, a wet weather pattern is expected
to unfold across the northeastern Caribbean as a mid-to-upper-
level trough moves from the northwestern to the north-central
Caribbean, while a deep layered ridge builds and holds just east
of the Leeward Islands. This will promote divergence aloft and
south-to-southwesterly wind flow at lower levels. Furthermore,
global models are indicating the development of an elongated area
of low pressure to our north/northwest through the first part of
the week. In response, moisture pooling is generally expected
across the local area through most of the long-term period, with
guidance suggesting 2.00-2.50 inches of precipitable water
content, peaking by midweek. Therefore, the risk of flooding rains
will significantly increase across all the islands.

As the southerly winds and high humidity persist, we can expect
warm to hot conditions across the islands, particularly across St.
Croix and most coastal municipalities of PR, on Monday. Afterward,
it will depend on how much cloud cover and rainfall materialize
over the islands. A drying trend is expected by Friday as the
broad surface ridge becomes the dominant weather feature.

&&

AVIATION...

(18z TAFs)

Mainly VFR conds expected across all local terminals. SAL will
continue to spread across the region today, causing hazy skies and
reduced VIS at times. Aftn SHRA/TSRA may cause brief tempo MVFR
conds at TJBQ through 31/22z and between 01/16-22Z at TJSJ/TJBQ.
Winds will prevail from the ESE at 10-15 kts with higher gusts and
sea breeze variations, becoming light to calm and variable between
31/22Z and 01/13Z.

&&

.MARINE...

A moderate east to southeast wind flow will prevail across the
region through Saturday, becoming easterly briefly on Sunday, and
with a dominant southerly component through midweek next week.
Thunderstorms are expected to develop through the weekend between
the late afternoon and evening hours across the western waters of
Puerto Rico. A wetter pattern is anticipated by Sunday into early
next week as the next tropical wave will approach the region with
increasing winds and seas across the Caribbean waters.

&&

.CLIMATE...

A new record daily maximum was set on the last day of May, when the
high reached 94F. In total, four daily maximum records were set this
month, as well as 15 daily warmest minimum. This month ended as the
warmest May on record for the San Juan Area climate site, with an
average temperature of 84.4F. The previous record was 84.1F set in
2020.

&

.BEACH FORECAST...

A low risk of rip currents will continue tonight across most
beaches of Puerto Rico, St. Thomas, and St. John while a moderate
risk is expected across southwestern Puerto Rico, Vieques, and St.
Croix. The risk of rip currents is expected to remain between low
and moderate throughout the upcoming weekend.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 5 PM AST this afternoon for PRZ001-005-008-
     010-011.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ002.

AM...None.

&&

$$

SHORT TERM/MARINE/BEACH FORECAST...YZR/RAM
LONG TERM....DSR
PUBLIC...RC
AVIATION...ICP/RAM
CLIMATE...ERG