856
FXCA62 TJSJ 090819
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
419 AM AST Wed Apr 9 2025

.SYNOPSIS...

A surface high pressure building in the Central Atlantic will
strengthen the local pressure gradient, promoting breezy easterly
winds for the next few days. Variable weather conditions will
continue through the end of the work week, becoming more wet and
unstable by the weekend. A long period northeasterly swell will
continue today, deteriorating marine and coastal conditions with
large breaking waves between 9 to 13 feet along north-exposed
beaches of Puerto Rico.

&&

.SHORT TERM...Today through Friday...

An easterly perturbation brought some showers across the surrounding
waters of the Virgin Islands, moving inland at times. However, the
Doppler Radar detected more frequent showers moving across the
eastern windward locations of PR. The winds overnight were mainly
from the east to east-southeast, between 5 and 10 mph, with land
breeze variations. Minimum temperatures reached the low 60s along
mountains and valleys, while the thermometer across coastal
locations reached the low 70s in some locations.

A surface high-pressure building across the Central Atlantic will
strengthen the local pressure gradient, promoting breezy easterly
winds. Additionally, a mid to upper-level ridge building from the
west near the Northeast Caribbean will replace a trough that will
exit into the Atlantic. This trough aloft will induce low-level
perturbations pushed into the region of PR and the USVI by the
easterly winds, resulting in occasional showery conditions,
especially across the windward locations through Thursday. As low-
level winds range from the east to east-southeast, afternoon
convection will develop across the southwest quadrant of PR today.

A long-period northeasterly swell creates hazardous breaking waves
and life-threatening rip currents along the north and east-facing
beaches in PR and the US Virgin Islands. Therefore, a High Surf
Advisory with a High Risk of Rip Current is in effect for the north-
facing beaches of PR, Culebra, and St Croix, and a High Risk of Rip
Current statement is in effect for the northern US Virgin Islands.

An approaching frontal boundary and a pre-frontal trough will
enhance moisture pooling over the islands on Thursday and Friday,
increasing the frequency of showers across the region, especially
around Friday afternoon. Although we can anticipate periods with
sunshine (daytime) and mostly clear skies (nighttime), we expect a
wet and rainy Thursday and Friday for some portions of PR. Flooding
rains may affect the windward sections of eastern PR as well as the
west quadrant, with the risk of the formation of the "San Juan
Streamer" downwind from El Yunque.

.LONG TERM...Saturday through Tuesday...

The remnants of an old frontal boundary in combination with an
induced low-level trough will promote unstable and wet conditions
throughout the fist-half of the long-term period. Latest model
guidance continues to suggest above-than-normal precipitable water
values (1.8 to 1.9 inches) from Saturday into Sunday. Therefore,
there is the potential to observe an increase in shower frequency
across the islands during this period. The overall weather pattern
has not changed from previous discussion, and the forecast
continue on track. The combination of the available moisture,
daytime heating and local effects will result in afternoon
convective activity across portions of the interior and western
Puerto Rico each day. This will increase the potential to observe
localized flooding, especially over urban and low-drainage areas.
By early next week, a mid-level ridge will build and place over
the region, promoting stability aloft. However, patches of
moisture will move from time to time over the area, bringing quick
moving showers over portions of the islands. By late Monday into
Tuesday a frontal boundary will approach the region from the west
bringing additional moisture and shower activity into the area.
Overall, winds will prevail mainly from the east southeast and
shifting from the east northeast from Monday onwards. The 925mb
temperatures will remain at normal or above-normal climatological
values during the period. Warm to hot conditions with heat indices
over the 100s degrees Fahrenheit are likely during the period.

&&

.AVIATION...
(06Z TAFs)

VFR conditions will persist thru the forecast period. Occasional
SHRA/-SHRA may impact IST/ISX/JSJ at times. However, there is a
moderate risk of observing MVFR conditions at TJBQ between 09/16-23z
and a low risk near JSJ if the San Juan streamer develops. SHRA/TSRA
will create low visibility and mountain obscurations during the
afternoon. Winds will be mainly calm to light and variable through
09/13z, returning from the E-ESE at 15-20 with higher gusts and sea
breeze variations, but gusty near TSRA/SHRA.

&&

.MARINE...

A broad surface high pressure over the western Atlantic will
continue to promote moderate to locally fresh easterly winds for the
next few days. A long period northeasterly swell is increasing seas
and deteriorating marine conditions and will continue throughout the
rest of the workweek. A Small Craft Advisory is in effect for the
offshore and coastal Atlantic waters and the Anegada Passage through
this evening.

&&

.BEACH FORECAST...

A long period northeasterly swell will continue to arrive across
beaches along the northern coast of Puerto Rico. The peak of the
event will continue through this afternoon with large breaking
waves between 9 to 13 feet, and occasionally higher. This will
result in life-threatening rip currents and beach erosion in
vulnerable areas. Therefore, a High Surf Advisory is in effect through
6 PM AST today and a High Rip Current Risk remains in effect
through late tonight. Please, heed the advice of lifeguards,
beach patrol flags and signs.


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through late tonight for PRZ001-002-005-
     008-012.

     High Surf Advisory until 6 PM AST this evening for PRZ001-002-
     005-008-012.

VI...High Rip Current Risk through late tonight for VIZ001-002.

     High Surf Advisory until 6 PM AST this evening for VIZ002.

AM...Small Craft Advisory until midnight AST tonight for AMZ711-712.

     Small Craft Advisory until 6 PM AST this evening for AMZ716-723.

&&

$$

SHORT TERM...CAM
LONG TERM....GRS