271
FXCA62 TJSJ 242051
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
451 PM AST Fri May 24 2024

.SYNOPSIS...

Isolated to scattered showers are expected overnight across the
eastern portions of Puerto Rico and the U.S. Virgin Islands. A wet
and unstable weather pattern is expected to prevail through next
week as a tropical waves approaches the local area from the
southeast on Monday. Warm and hot temperatures will persist, with
heat indices reaching the upper 100s mainly across the urban and
coastal portions of the islands.

&&

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

Fair weather conditions prevailed during the morning hours under
partly to mostly cloudy skies. Warm conditions were observed,
once again, across the region due to southerly winds and the
influence of a deep-layered trough over the Dominican Republic.
The Luis Munoz Marin Int. Airport reported a maximum temperature
of 91 degrees Fahrenheit. Across the local islands, daytime
temperatures were observed in the upper 80s to low 90s mainly
along the coastal and urban areas. Heat indices between 110-112
degrees Fahrenheit were observed across the north-central and
southwestern portions of Puerto Rico.

Late afternoon convection developed over portions of central and
southwestern Puerto Rico. Showers and isolated thunderstorms
affected mostly the San German area, where doppler radar estimated
accumulations up to 3.0 inches of rain. This activity should
gradually dissipate by the early evening hours. By Saturday into
Sunday, a mid-level ridge will continue to move eastward as the deep-
layered trough weakens. However, sufficient available moisture
will enhance showers and isolated thunderstorms across the
interior, northern and northwestern portions of Puerto Rico each
afternoon. Slow-moving showers could enhance the risk of flooding
in flood- prone areas. Therefore, the risk of flooding remains
limited to elevated through the rest of the period. Despite the
anticipated weather conditions, daytime temperatures will continue
in the upper 80s to lower 80s across much of the area. Expect
these conditions to prevail until early next week until the
arrival of a tropical wave. Heat indices could reach the upper
100s, where a Heat Advisory may be issued in those areas during
peak hours of the day before shower activity begins. Stay hydrated
if engaging in outdoor activities.

.LONG TERM...Monday through Friday...

PREV DISCUSSION.../issued 544 AM AST Fri May 24 2024/

Model guidance indicates that a wet pattern will persist through the
long-term forecast due to a moist airmass across the region as a
tropical wave approaches from the east. As this tropical wave
moves over the islands by late Monday, causing moisture content
to rise above 2.0 inches, an increase of unstable weather is
expected to last through the long term period. Weak ridging aloft
throughout the week will help keep conditions somewhat decent,
yet the continuation of the passage of weak short-wave troughs
through Friday will maintain above-normal moisture and marginal
instability.

The National Blend of Models hints for heavier rainfall during the
afternoon hours particularly across western/northwestern Puerto Rico
under an east-southeast steering flow. The Galvez-Davison Index also
suggests a similar scenario, with a high potential for observing
isolated to scattered thunderstorms capable of producing heavy
rainfall each day. With saturated soils and elevated streamflows
from previous days of rainfall, the flooding risk will remain
elevated. Therefore, we could expect urban and small stream
flooding, as well as flash flooding and landslides in areas of steep
terrain.

Hot days are also to be expected with heat indices reaching in the
100s to 110s through the week due to the high RH values and heating
from the summer sun, therefore heat advisories or warnings may be
issued during this time. Saharan dust particulates are expected to
arrive by early in the week. Expect hot and hazy conditions to
prevail across sections with less rainfall.


&&

.AVIATION...

(18z TAFS)

Mainly VFR conds will prevail across all terminals through the
forecast period. Afternoon convection will develop along and north
of the Cordillera Central affecting local terminals, especially
JBQ/JSJ. SHRA/TSRA downwind from the USVI may create MVFR conds at
IST/ISX thru this evening. Also, SHRA/TSRA en route from the Mona
Passage and E-Caribbean could reach portions of USVI/ PR overnight.
Surface winds will continue from the ESE at 5-15 kt but locally
higher due to gusty winds and sea breeze variations.

&&

.MARINE...

Surface high pressure across the central and northeast Atlantic and
an induced surface trough just northwest of the region will promote
moderate southeast winds through late tonight. In addition, the
proximity of a deep layer trough over the Dominican Republic and an
easterly disturbance will aid in enhancing thunderstorm development
across portions of the regional waters and local passages through at
least this evening. Winds are forecast to diminish overnight and then
become more easterly over the weekend.

&&

.BEACH FORECAST...

Seas will remain below 5 feet across much of the regional waters.
Therefore, there is a low risk of rip currents across the local
beaches of Puerto Rico and the U.S. Virgin Islands.


&&

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

$$

SHORT TERM...RAM
LONG TERM....GRS
AVIATION...CAM
PUBLIC DESK...LIS