549
FXCA62 TJSJ 271825
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
225 PM AST Fri Jun 27 2025

.KEY MESSAGES...

 *Sunday is expected to be the wettest day in the short-term forecast.

 *Windy conditions will remain in place through tonight and into Saturday.

 *Another surge of Saharan dust is expected to arrive across the
  islands by Monday.

&&

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

Variable weather conditions prevailed during the morning hours,
with brief showers observed across eastern Puerto Rico and the
U.S. Virgin Islands, and cloudiness affecting the rest of the
region. Around 11 AM, additional showers developed over the
mountainous areas, producing limited to moderate rainfall with
minimal accumulation. Winds from the east-northeast (E-NE) helped
steer these showers over the interior and southern coastal plains
of Puerto Rico. Daytime temperatures reached or slightly exceeded
climatological normals across some coastal areas, surpassing 90F,
while cooler conditions persisted in the mountains. Heat indices
peaked near 106F in isolated locations during the mid-morning
hours. For the remainder of the night, variable conditions will
continue as E-NE winds transport patches of fragmented cloudiness
across northeastern Puerto Rico and the USVI. In the upper levels,
a trough will maintain some instability over the region, resulting
in occasional passing showers. Although rainfall accumulations
are not expected to cause flooding, they may temporarily reduce
visibility and create hazardous driving conditions.

On Saturday, a mid- to upper-level ridge moving from east to west
will become established over the CWA, promoting a mostly stable
weather pattern. However, localized afternoon convection remains
possible across the western interior sections of Puerto Rico due
to daytime heating and local effects. By Sunday, weather
conditions are expected to deteriorate significantly as a tropical
wave approaches and moves across the region. This system will
bring a notable increase in deep tropical moisture and cloudiness,
enhancing the potential for widespread showers and isolated
thunderstorms throughout the day. Precipitable water values are
expected to climb above seasonal normals, favoring efficient
rainfall processes. Winds will shift to an east-southeasterly
direction in response to a weakening surface ridge over the
central Atlantic, which will help channel moisture across the
region and provide favorable low-level convergence. As a result,
the most significant rainfall activity is expected to develop
across the interior and northwestern portions of Puerto Rico,
including the San Juan metropolitan area. While flooding is not
currently anticipated, persistent or heavier showers could lead to
ponding of water on roadways and minor urban flooding in poor
drainage areas.

.LONG TERM...Monday through Friday...
from previous discussion...

A mid-level ridge will build and hold over the northeast
Caribbean by early next week, establishing a strong trade wind
inversion that will promote subsidence and a drier atmosphere
aloft, significantly limiting deep convective development through
midweek. At the same time, a Saharan Air Layer (SAL) arrived
behind Sunday`s tropical wave, resulting in hazy skies, degraded
air quality, and reduced visibility from Monday through at least
Tuesday. Once again, model guidance indicates a tropical wave
moving well south across the southern section of the Caribbean,
leaving the islands under the influence of pockets of moisture
embedded within easterly trade winds.

The ridge aloft will weaken around Wednesday as the dry air mass
leaves the region, and a retrograding mid- to upper-level
trough/low moves closer to the islands, inducing perturbations at
the surface. As the trough retrogrades toward the Northeast
Caribbean, it will induce perturbations in the surface that will
be pushed by the trades at times. However, a tropical wave is
expected to arrive, increasing the moisture content by late
Thursday night or Friday and transitioning into a more unstable
weather pattern.

Temperatures are expected to trend above normal, especially under
the influence of the SAL, which will reduce overnight cooling and
result in warmer minimum and maximum temperatures across the
islands.

&&

.AVIATION...

Brief MVFR conditions will remain in place until 27/23Z during RA
to SHRA resulting in lower VIS and lower flight ceilings. Winds
will remain from the E-NE up to 15 knots and gusty winds,
decreasing at 27/23Z and peaking again by 28/14-28/15 from the E
with gusty winds.

&&

.MARINE...

A surface high pressure over the central Atlantic will promote
moderate to fresh easterly winds, resulting in choppy seas across
the local Atlantic and Caribbean waters. Mariners should prepare
for deteriorating marine conditions as a trade wind perturbation
arrives today, increasing the potential for showers and
thunderstorms. Additionally, a tropical wave is expected to move
into the region late Saturday night into Sunday, which may further
enhance convective activity and hazardous marine conditions.


&&

.BEACH FORECAST...

There is a moderate risk of rip current across the northern,
southeastern and eastern PR including Vieques, Culebra and the
U.S. Virgin islands. The risk will become low for most of the
coastal areas on Saturday, except for the northwestern areas of PR
and St. Croix.

&&

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

$$

SHORT TERM...Morning Crew
LONG TERM....Midnight Crew