044
FXCA62 TJSJ 021928
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
328 PM AST Sat Aug 2 2025

.KEY MESSAGES...

* With the axis of the tropical wave now over the Mona Passage,
  southeasterly flow will continue to steer abundant tropical
  moisture over the islands through at least Sunday.

* Low to moderate concentrations of Saharan dust are expected to
  arrive from the east on Sunday night into early Tuesday, leading
  to hazy skies and deteriorated air quality.

* Southeasterly flow and high humidity will also increase heat
  index values. Heat Advisories, or even Warnings, cannot be ruled
  out during the workweek.

&&

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

A tropical wave crossing the area promoted variable to showery
weather over most of the region today. Radar estimated rainfall
accumulations since midnight show most of the region with
measurable rainfall. As of 2 PM AST, the highest accumulations
were observed over Yabucoa, with up to 2.5 to 2.8 inches in
several sectors of the municipality. Radar estimated accumulations
above 2 inches were also observed over Corozal and Maunabo. Radar
estimated accumulations above 1.5 inches were observed over
Vieques, Rio Grande, Morovis and Aguadilla. Several thunderstorms
were also observed over the waters, with Marine Weather Statements
being in effect through most of the day. Heat indices still
climbed over the 100s over several areas, particularly the SW
quadrant of PR and the USVI. As the axis of the wave moved over
the area (currently over the Mona Passage), southeasterly steering
flow gradually started to dominate. This steering flow will
continue to bring tropical moisture over the area with
precipitable water (PWAT) values remaining above 2 inches through
at least Sunday night, with PWAT values sharply decreasing on
Monday, as more humid air is confined to the lower levels, a stark
difference from the weekend. Showers, and isolated thunderstorms
will continue to be steered by southeasterly flow tonight,
reaching windward sectors of the islands. Low temperatures can
reach the the upper 70s to low 80s at coastal and urban areas, and
the upper 60s to low 70s at higher elevations. Additional
convection will continue to develop tomorrow afternoon and Monday
afternoon (here more limited), particularly from interior to
northwestern Puerto Rico, and downwind of El Yunque and the local
islands. A limited to locally elevated flooding risk will continue
tomorrow. By Monday, a strengthening low- to mid-level ridge will
establish itself as a plume of Saharan dust also arrives,
resulting in hazy skies to start the workweek. 925 mb temperatures
will continue at near to above normal values.

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

/FROM PREV DISCUSSION...Issued at 310 AM AST Sat Aug 2 2025/

The long-term forecast begins with lingering instability aloft as an
upper-level low continues to exit the forecast area. Although cooler
500 mb temperatures will lead to steeper lapse rates, below-normal
moisture levels will somewhat limit shower activity across the
region. Nevertheless, surface heating, sea breeze convergence, and
orographic lifting will be sufficient to compensate for the reduced
moisture, resulting in afternoon convection over interior and
western portions of Puerto Rico. Elsewhere, lingering suspended
Saharan dust will lead to hazy skies and limited shower activity.

Dynamic instability will persist on Wednesday as an induced surface
trough moves westward and crosses the northeastern Caribbean. The
areal coverage of showers and thunderstorms is expected to increase
during this period, aided by near-normal moisture converging in the
region.

For the remainder of the long-term forecast, weather conditions will
be variable, with marginal instability. This will be due to a series
of weak troughs crossing the region, combined with below-to-near-
normal moisture content. Alternating periods of fair weather,
showers, and thunderstorm activity will follow the typical seasonal
weather pattern. Showers will move onshore at times over windward
coastal areas during the night and morning hours, while shower and
thunderstorm development is expected over the interior and western
portions of Puerto Rico during the afternoon. The southern coastal
areas of Puerto Rico are likely to continue experiencing abnormally
dry conditions throughout the period, with only occasional, isolated
showers, which are likely to be insufficient to bring significant
relief to the region.

The forecast period will also be characterized by hot temperatures,
as 925 mb temperatures fluctuate between near-normal and above
climatological normals. These above-normal temperatures, combined
with humid conditions, will result in persistently high heat index
values. As a result, Heat Advisories, or even Warnings, cannot be
ruled out throughout the period. Residents and visitors are advised
to stay hydrated, limit outdoor activities during peak heat hours,
and monitor official updates for potential heat-related alerts.

&&

.AVIATION...

(18Z TAF)

The axis of the tropical wave is over the Mona Passage, with
ESE winds now prevailing over the islands, with sea breeze
variations and local effects. TSRA will affect TJBQ through at
around 03/20Z. ESE winds (at light to locally moderate) continue
to bring showers and possible thunderstorms over the area, these
can promote brief periods of MVFR conditions from time to time.

&&

.MARINE...

A surface high-pressure over the central Atlantic, combined with
a tropical wave moving away from the islands, will promote
moderate to locally fresh winds through the weekend. Seas of up to
7 ft are likely for the offshore Atlantic waters where a Small
Craft Advisory is in effect through this evening. Although the
axis of the tropical wave is over the Mona Passage, southeasterly
steering flow behind it will bring abundant tropical moisture over
the waters, promoting showers and t-storms during the rest of the
weekend. Hazy skies due to the arrival of Saharan dust are
anticipated Monday.

&&

.BEACH FORECAST...

A moderate risk of rip currents will continue during the weekend for
northern and eastern PR, as well as Culebra and St. Croix, with a
low risk elsewhere. Even if the risk for rip currents is low,
life-threatening rip currents often occur in the vicinity of
groins, jetties, reefs, and piers. Abundant moisture from a
tropical wave moving away from the islands can result in showers
and t-storms under southeasterly flow. Deteriorated air quality
is forecast for Monday as a plume of saharan dust moves in.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...Small Craft Advisory until 6 PM AST this evening for AMZ711.

&&

$$

MRR/RVT/ERG/MNG