204
FXCA62 TJSJ 241906
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
306 PM AST Tue Jun 24 2025

.KEY MESSAGES...

* Moderate to high concentrations of Saharan Dust are expected
  from today through at least Thursday night. Hazy skies and poor
  air quality are expected.

* Daily afternoon showers and isolated thunderstorms are expected,
  particularly over northwestern Puerto Rico due to local
  effects.

* By the end of the week into the weekend, a TUTT-low is forecast
  to develop just north/northeast of the region, and another
  tropical wave is expected to enter the eastern Caribbean.

&&

.SHORT TERM...Tonight through Thursday...

Starting off the day, we observed showers across sectors of eastern,
southeastern, and east-central Puerto Rico, with radar- estimated
maximum rainfall accumulations ranging between 0.30 and 0.60 inches
with no significant impacts. The 12Z sounding showed 1.88 inches
of precipitable water, indicating moisture from the tropical wave
moving to our south. Those values are average for this time of the
year. Breezy winds with an east-southeast component have prevailed,
reaching speeds of 15 to 25 mph, with higher gusts. The strongest
gusts were recorded in coastal areas, ranging from the upper 20s
to low 30s mph. Heat indices exceeded 108F in northern and western
Puerto Rico, prompting a Heat Advisory in effect until 5 PM AST.
Tonight, partly cloudy skies and hazy conditions will persist,
with latest model suggesting some isolated showers across western
areas of Puerto Rico.

From now through Thursday, drier air and moderate to high
concentrations of Saharan dust will continue to filter into and
dominate the region. This will lead to limited rain chances but
also warmer temperatures. Fewer and more localized afternoon
showers and isolated thunderstorms are still possible, mainly
driven by local effects. However, the flood threat remains from
none to limited. Main weather concern will be the hazy skies,
reduced visibility, and poor air quality, especially for sensitive
groups, such as individuals with respiratory conditions. The
event is expected to peak today and continue into Wednesday, with
another peak likely on Thursday, before conditions gradually
improve on Friday onward across Puerto Rico and the US Virgin
Islands. Additionally, above average temperatures will likely
persist over the next several days, with 925 mb temperatures in
the above normal range for this time of the year, especially
across coastal and urban areas of the islands. In combination with
southeasterly breezy winds will aid the continuation of warm
conditions. Please stay hydrated and stay alert for forecast
updates and the possible issuance of additional Heat Advisories,
especially heat- sensitive individuals, including those without
adequate cooling or hydration.

.LONG TERM...Friday through Tuesday...
.PREV DISCUSSION... /issued 520 AM AST Tue Jun 24 2025/

The inherited forecast remains on track, with a TUTT-low expected to
develop just north to northeast of the region between Friday and
Saturday. During this period, an induced surface trough will move
across the area, shifting winds from the east-northeast. This
shift will favor the development of afternoon showers, primarily
across the southwestern quadrant of Puerto Rico. Across the U.S.
Virgin Islands and eastern Puerto Rico, shower activity is
expected to increase mainly during the nighttime hours. Despite
this, precipitable water values are forecast to remain near
climatological normals, and 500 mb temperatures will range from
the 50th to 75th percentile. These factors suggest that while some
moisture and instability will be present, conditions will not be
particularly favorable for deep convective development or
widespread thunderstorm activity. On Saturday, lingering moisture
and the onset of east-southeasterly winds behind the trough will
once again support afternoon shower development, especially across
the northwestern quadrant of Puerto Rico and downwind of El
Yunque. A tropical wave is then expected to quickly follow,
entering the eastern Caribbean between late Saturday and Sunday
morning. This feature will enhance moisture and instability,
likely increasing the areal coverage of showers and thunderstorms
across portions of the islands and surrounding local waters.

&&

.AVIATION...
(18Z TAFs)

VFR conditions are mainly expected during this forecast period,
although with HZ and visibilities from 5-8SM due to Saharan Dust.
VCSH possible over eastern sites during the period. VCTS are
possible after 25/17Z across TJBQ. E-ESE winds up to around 15-20
kts with sea breeze variations and higher gusts will continue
through 24/23Z. Winds decreasing to around 9-15 kts, with higher
gusts, after 24/23Z before increasing again after 25/13Z to 15-20
kts with higher gusts and sea breeze variations.

&&

.MARINE...

A subtropical Atlantic ridge extending southward into the northern
Caribbean continues to promote moderate to fresh easterly winds,
resulting in choppy seas over portions of the local Atlantic and
Caribbean waters, and local passages. Therefore, small craft should
exercise caution. Past tropical wave over the Caribbean Sea will
continue to leave cloudiness and some shower activity across the
across the local waters this afternoon. Hazy and drier conditions
over the next few days.

&&

.BEACH FORECAST...

Wave heights of around 3 to 5 feet and a moderate risk of rip
currents are expected tonight along most beaches of Puerto Rico,
including Vieques, Culebra, and the U.S. Virgin Islands. A
moderate risk indicates that life-threatening rip currents are
possible in the surf zone. As a result, beachgoers are encouraged
to exercise caution. Similar conditions are expected to continue
over the next few days.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 5 PM AST this afternoon for PRZ001-005-008-
     010.

VI...None.
AM...None.
&&

$$

SHORT TERM/AVIATION...YZR/MRR
LONG TERM...MMC