444
FXCA62 TJSJ 080918
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
518 AM AST Wed Jan 8 2025

.SYNOPSIS...

Today, an increase in moisture from the Caribbean accompanied by
light winds will lead to frequent passing showers during the
morning and additional showers development during the afternoon
hours over interior and northwestern Puerto Rico. The proximity of
a frontal boundary will promote more frequent showers and
northerly winds by the end of the week, resulting in fresh
temperatures across the islands. A stable weather pattern will
prevail through the weekend into early next week with drier
airmass dominating behind the front. A fading long-period
northerly swell and additional pulses will continue to result in
hazardous marine and coastal conditions across the Atlantic Waters
and the exposed north-facing beaches today and Thursday. Another
northerly swell will further deteriorate marine and coastal
conditions from Friday onward.

&&

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

During the overnight hours into the early morning, stable
atmospheric conditions prevailed across the region. However, some
passing showers affected the northern sections of Puerto Rico and
the Caribbean Waters. Winds persisted from the east at 10 knots or
less, maintaining calm conditions. Overnight temperatures were in
the low 80s across coastal areas, with slightly cooler readings
observed in the mountainous regions.

For today, an interesting weather pattern is unfolding as a
weakening surface high-pressure system becomes influenced by a pre-
frontal trough associated with an approaching frontal boundary to
the north of the region. This setup will result in light east-
southeast winds dominating much of the day. GOES-derived imagery
indicates an increase in moisture from the Caribbean, with
precipitable water (PWAT) values near 1.5 inches. This moisture
surge is expected to linger throughout the day, leading to frequent
passing showers in the morning and additional convective development
during the afternoon hours, particularly over interior and
northwestern Puerto Rico.

Looking ahead to Thursday and Friday, weather conditions will be
increasingly influenced by the pre-frontal trough moving into the
region. This feature will weaken the pressure gradient, resulting in
lighter and more variable winds. Pockets of moisture will persist
across the area, with the best potential for showers focusing over
the interior sections due to the lack of significant steering flow.
By Friday, global model guidance continues to support the passage of
the frontal boundary (FROPA). This pattern will introduce northerly
winds and much drier air, significantly improving overall weather
conditions and colder temperatures for the upcoming weekend.

&&

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

The long-term period will primarily be characterized by stable
weather conditions. On Saturday, a much drier air mass behind the
front will dominate the forecast area, leading to slightly cooler
and more stable weather throughout the period. With a surface
high-pressure system located to the north, winds will shift to
the northeast on Saturday and gradually weaken from Sunday into
the beginning of the week.

Overall, the combination of limited moisture and the presence of a
mid-level ridge, which creates a trade wind cap inversion, will
prevent significant rainfall. If any rain occurs, it will likely
be during the mornings in northern or eastern areas of Puerto
Rico. As a result, expect mostly sunny skies and minimal rainfall
during the day, providing favorable conditions for outdoor
activities. According to the latest model guidance, a weak front
will approach the region by midweek, slightly increasing northerly
to northeasterly winds and the probability of precipitation.
Pleasant temperatures are expected to prevail, daytime highs
should peak in the low to mid 80s along the coast and urban areas,
and in the low to mid-70s in the mountainous regions. Minimum
temperatures in the 70s and 60s across the same areas,
respectively.

&&

.AVIATION...
(06Z TAFs)

VFR conditions will persist for all the TAF sites during the
period. Winds will continue from the E-SE at 10 knots or less, with
sea breeze variation and some gusty winds near strong showers. VCSh
to -RA is forecast today across the interior, and that would result
in lower ceiling and VIS affecting some lower flight levels.

&&

.MARINE...

A cold front extending from the Western Caribbean into the Western
Atlantic will move southeastward, approaching the region around mid-
week. As the frontal boundary with its associated pre-frontal trough
approaches the islands, expect light to moderate winds from the
east-southeast today and Thursday. Behind the front, winds will turn
moderate to locally fresh from the north between late Thursday and
Friday, then return from the northeast by Saturday. A fading long-
period northerly swell is still spreading across the Atlantic waters
this morning and another pulse is expected tomorrow. By the end of
the week into the weekend, building seas are anticipated as a stronger
northerly swell spread across the local waters and passages.

&&

.BEACH FORECAST...

Beachgoers, breaking waves around 5 to 7 feet continues to create
life-threatening rip currents across the northern exposed
beaches of Puerto Rico, including Culebra, St. Thomas and St.
John in the U.S. Virgin Islands at least through this afternoon.
We encourage residents and visitors to monitor the forecast as
another pulse will likely continue to promote life-threatening rip
currents along the same areas and the risk will need to be
extended. By the end of the week into the weekend, a stronger
northerly swell spread across the local waters and passages
maintaining hazardous coastal conditions. The risk should remain
from low to moderate along southern protected beaches.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through this afternoon for PRZ001-002-005-
     008-010-012.

VI...High Rip Current Risk through this afternoon for VIZ001.

AM...None.
&&

$$

SHORT TERM/AVIATION...LIS
LONG TERM/MARINE/BEACH...YZR