066
FXCA62 TJSJ 021911
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
311 PM AST Wed Jul 2 2025

.KEY MESSAGES...

* Passing showers and gusty winds will continue this afternoon and
  tonight as patches of moisture continue to move into the
  region.

* A weak tropical wave is anticipated to arrive on Friday, followed
  by the presence of Saharan dust resulting in hazy skies and
  deteriorating air quality conditions.

* Anticipate seasonably hot temperatures each day, with afternoon
  heat indices over 100 degrees.


&&

.SHORT TERM...Tonight through Friday...

A trade wind perturbation resulted in an increased frequency of
showers moving over eastern portions of Puerto Rico and smaller
islands during the morning hours. These showers moved fairly
quickly; however, they still left close to an inch of rain in those
southeastern municipalities of Puerto Rico. By late morning to early
afternoon, the trade wind perturbation continued to promote shower
development, mostly over the northern half of Puerto Rico,
particularly over the northwestern quadrant. These showers left
about an inch of rain in very localized areas, such as northern
Bayamon. Expect a continuation of these showers and possible
isolated thunderstorms during the afternoon hours as surface heating
and local effects aid in convective development. Additionally,
breezy wind conditions were also reported. By noon, gusty wind
conditions had already been observed, with several coastal weather
stations recording sustained winds in the upper 20s and low 30s mph
range. The La Puntilla tide weather station even reported wind gusts
reaching 33 mph.

The mid-level ridge that has been influencing us continues to erode
due to a mid-to-upper level low approaching from the northeast.
Meanwhile, high pressure over the central Atlantic will maintain a
breezy east-southeast steering flow for most of the period. However,
a slight dip in wind speeds is likely tomorrow before conditions
return to breezy.

While drier air moves in on Thursday, by late Thursday into early
Friday, moisture from a tropical wave will start to increase PWAT
values once more. The wave itself will cross our area later on
Friday, bringing PWAT values up to around 2 inches. However, a wind
surge behind the wave and moderate to high amounts of Saharan Dust
are weakening the tropical wave, which will potentially limit its
impacts. Despite these features, the increased moisture should
trigger showers across the islands under the east-southeast flow,
with stronger convection developing over western and northwestern
Puerto Rico and downwind of the islands and El Yunque in the
afternoon. Be aware of a limited heat threat that will persist
across urban and coastal areas during the late morning to afternoon
hours. Drink plenty of fluids, limit strenuous outdoor activities,
and take frequent breaks in the shade.

.LONG TERM...Saturday through Wednesday...

/From Prev Discussion issued at 436 AM AST Wed Jul 2 2025/

Surface high pressure over the central Atlantic will maintain
fresh trade winds across the region. At the lower levels, a dense
Saharan Air Layer will move into the islands, resulting in hazy
skies on Saturday and Sunday. Some leftover moisture will also be
available, so some passing showers will continue as well. For the
workweek, not many changes are anticipated, with a trade wind cap
inversion around 850 mb, and all the available moisture trapped
near the surface. A couple of weak tropical wave will move across
the region, but also some patches of light to moderate amounts of
Saharan dust as well. The weather pattern will be variable, with
passing showers over the Virgin Islands and eastern Puerto Rico,
and afternoon convection in western Puerto Rico. No significant or
widespread flooding is expected during the forecast period.
However, it will be hot, with the guidance forecasting heat
indices above 102 degrees for all coastal and urban areas of the
islands each afternoon.


&&

.AVIATION...
18Z TAFS)

Mostly VFR conditions expected to continue. SHRA/TSRA will continue
across northwestern PR through 21Z, with brief periods of low
ceilings and reduced VIS  possible at TJBQ. Showers will taper off
after that. Winds will slow down, below 10-12 knots after 22Z, but
will speed up after 03/14Z, out of the ESE at 10-15 kts, with
stronger gusts.

&&

.MARINE...

Choppy seas are expected to continue across the local Atlantic and
Caribbean waters due persistent moderate to fresh easterly winds.
A weak tropical wave is forecast to move over the local waters on
Friday, increasing shower and thunderstorm chances. Saharan dust will
follow the tropical wave, with hazy skies returning on Saturday and
Sunday.

&&

.BEACH FORECAST...

Wind-driven seas will maintain a moderate risk of rip currents
along most exposed beaches of the islands through much of the
forecast period, although will diminish somewhat by the end of the
week.

&&

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

$$


CVB/MMC