233
FXCA62 TJSJ 261857
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
257 PM AST Sat Jul 26 2025

.KEY MESSAGES...

* Lingering concentrations of Saharan dust will persist through at
  least this evening.
* Showers and isolated thunderstorms will continue through this
  evening, increasing flooding potential mainly over western Puerto
  Rico.
* A limited to elevated flooding threat will be present on Sunday
  and Monday due to the arrival of two tropical waves across the
  forecast area.

&&

.SHORT TERM...Tonight through Monday...

Very tranquil weather conditions prevailed during the morning hours,
with mostly sunny skies and only a few clouds moving over the area
from time to time. Some hazy skies were observed due to lingering
suspended Saharan dust particulates. Thanks to mostly clear skies,
temperatures rose to the upper 80s to low 90s across coastal areas
and the smaller islands. Although overall moisture content remained
lower than in previous days, there was still enough present to cause
heat index values to exceed 100F in those same areas. Doppler radar
detected scattered showers developing over portions of western
Puerto Rico due to surface heating and sea breeze convergence. This
activity is expected to persist through the evening hours, with a
few isolated thunderstorms possible.

The forecast remains largely on track with earlier discussions. GOES-
19 Total Precipitable Water satellite data indicates that the
leading edge of a broad tropical wave, with its axis currently near
61.3W, is already beginning to filter into the eastern portion of
the forecast area. According to the Tropical Analysis & Forecast
Branch (TAFB) surface analysis, the axis of the tropical wave is
expected to reach the U.S. Virgin Islands USVI by 27/12Z and the
Mona Passage by 28/00Z. As a result, expect a gradual increase in
cloud cover and shower activity by late tonight across the USVI,
Vieques, and Culebra. This activity is expected to reach the eastern
third of Puerto Rico by early morning, and, if cloud cover does not
significantly limit surface heating, the interior and northwestern
sections of Puerto Rico by the afternoon hours. Consequently, a
limited to elevated flooding threat is in place for the entire CWA
on Sunday, with the exception of southwestern Puerto Rico, where
only a limited flooding threat is anticipated.

On Monday, another tropical wave, though much weaker, will move
across the forecast area, extending the wet period across the
islands. However, the areal extent of the elevated flooding threat
will be more limited, primarily confined to eastern and western
Puerto Rico. Shower and thunderstorm development is expected to
follow a similar pattern, but activity will be more localized due to
the weaker nature of the wave.

As previously mentioned, the heat threat forecast remains
challenging, as it will largely depend on the extent of cloud cover.
Nevertheless, any coastal area that experiences reduced cloud
coverage will likely observe higher maximum temperatures, which,
when combined with well-above-normal moisture levels, will result in
at least a limited heat threat.


.LONG TERM...Tuesday through Saturday...
//from previous forecast//

A mid-level ridge pattern is expected to prevail across the local
islands throughout the forecast period, with some weakening
anticipated on Wednesday and Thursday. At lower levels, a surface
high-pressure northeast of the region will continue to yield
easterly winds for much of the cycle, with a tropical wave moving
across the eastern Caribbean during the weekend. In terms of
precipitable water, lingering moisture is expected on Tuesday,
with a sharp decrease on Wednesday. Although the trades will
continue to bring patches of moisture from time to time on
Thursday and Friday, deep tropical moisture advection is expected
from Saturday night into Sunday, associated with the passage of
the aforementioned tropical wave. Overall, Monday through at least
Friday, moisture will be confined below 850 mb. As a result,
Tuesday is expected to be a transitional day with afternoon
showers and thunderstorms developing across much of central and
western Puerto Rico. Once a drier airmass encompasses the area,
expect a seasonal weather pattern with afternoon showers and
isolated thunderstorms, mainly focused across west Puerto Rico on
Wednesday and Thursday. The intensity and areal coverage of
showers and thunderstorms are expected to increase once again over
the upcoming weekend, associated with the passage of the tropical
wave.

Having said this, the risk for urban and small stream flooding
is expected to increase by the end of the forecast cycle. Warm to
hot temperatures will continue to prevail with heat indices
exceeding 100 degrees each day. The hottest days are likely to be
Wednesday and Thursday. Some haziness is anticipated on Tuesday.

&&

.AVIATION...
(18Z TAFS)

VFR conditions are expected through the forecast period. Saharan
dust is causing slight HZ, but VIS will remain above 6SM. Brief
SHRA/TSRA possible near TJBQ throughout about 26/23Z.  A tropical
wave will cause SHRA/TSRA to affect the vicinity TISX, and TIST aft
27/23Z and 27/14Z, and TJSJ and TJBQ aft 27/14Z. Breezy to windy
conditions will persist, with sustained winds of 16-22 knots and
gusts up to 25-30 knots through 27/23Z, decreasing to 8-12 knots
overnight. Winds will increase again to 16-20 knots with higher
gusts aft 27/13Z.

&&

.MARINE...

A moderate to locally fresh easterly wind flow will continue to
prevail across the local waters during the weekend into early next
week. A tropical wave will reach the area late tonight into
tomorrow, increasing the chance for showers and thunderstorms,
particularly across the Caribbean waters and local passages. A
second tropical wave is forecast to arrive early next week.

&&

.BEACH FORECAST...

Beachgoers can expect a moderate risk of observing life-threatening
rip currents along the exposed beaches in the northwest coast of
Puerto Rico and Saint Croix. Culebra will become moderate by early
tomorrow. In contrast, elsewhere, can expect a low risk of rip
currents. Regardless of the low risk, isolated stronger rip
currents may occur, especially near piers, jetties, and channels.
A tropical wave will reach the area late tonight into Sunday,
increasing the chance for showers and thunderstorms.

&&

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

$$

SHORT TERM/AVIATION...CVB
LONG TERM/MARINE/BEACH FORECAST...MMC