483
FXCA62 TJSJ 281826
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
226 PM AST Tue Apr 28 2026

...New SHORT TERM, AVIATION, MARINE, BEACH FORECAST...

.KEY MESSAGES...
Updated at 222 PM AST Tue Apr 28 2026

* A limited to elevated flooding risk will continue for Puerto Rico
  this afternoon as showers and t-storms continue to develop mainly
  over interior to the northern half of Puerto Rico.

* Although showers and t-storms will gradually diminish after
  sunset, passing showers will continue across windward sectors.
  Another round of slow moving showers and t-storms is forecast to
  develop late tomorrow morning to afternoon.

* A moderate rip current risk continues over north and east-facing
  beaches Puerto Rico, Culebra and St. Croix for the next several
  days. This risk will possibly spread to the rest of the local
  islands later in the week.

* Up to a limited heat risk will continue across urban and coastal
  areas of the islands without prolonged rain and cloud coverage.

&&

.Short Term(This evening through Thursday)...
Issued at 222 PM AST Tue Apr 28 2026

During the morning hours, the most active portion of the remnants of
the frontal boundary remained across and east of St. Croix, where
periods of showery weather were observed, while widespread cloud
cover prevailed across much of Puerto Rico and the local waters.
This extensive cloudiness limited early daytime heating and
introduced some uncertainty regarding convective development for
this afternoon. However, gradual clearing developed by late morning,
allowing for surface heating and the onset of sea breeze
convergence, which quickly led to the development of showers and
thunderstorms around noon across portions of northern and
northeastern Puerto Rico. Additional clearing and daytime heating
will continue to support an active period through the afternoon.
Supporting this scenario, the 28/12Z TJSJ sounding indicated
precipitable water (PWAT) values near 1.95 inches, which remains
above climatological normals for this time of year. The sounding
also showed veering winds with height, colder temperatures aloft,
and very light winds through nearly 6 km, reflecting an unstable
environment favorable for thunderstorm activity.

The weak steering flow will favor slow storm motions, increasing the
potential for enhanced rainfall accumulations where heavy showers or
thunderstorms persist or repeatedly develop over the same areas.
Some of the strongest thunderstorms this afternoon could produce
frequent lightning, gusty winds, and isolated near-severe
thunderstorms. As a result, showers and thunderstorms are expected
to develop mainly across the interior and western/northwestern
sections of Puerto Rico during the afternoon, then drift slowly
toward surrounding municipalities. Given the weak steering flow and
abundant moisture in place, urban and small-stream flooding, ponding
on roadways, and localized flash flooding will remain possible
during the heaviest rainfall. Further landslides and rock falls
cannot be ruled out.

For tonight, convection will gradually diminish after sunset, but
lingering low-level moisture and nearby frontal remnants will
maintain passing showers across windward sectors of eastern Puerto
Rico and the U.S. Virgin Islands. Any overnight activity should be
brief, although locally heavy downpours cannot be ruled out. Minimum
temperatures will remain warm to muggy across coastal and urban
areas, with cooler readings across higher elevations.

On Wednesday, moisture content is forecast to remain above normal,
with precipitable water values near or above 2.0 inches while weak
steering flow persists. This pattern will favor another round of
showers and thunderstorms developing by late morning and through the
afternoon across the interior, western, and northern sections of
Puerto Rico. Given continued light winds, slow-moving thunderstorms
may once again produce excessive rainfall and localized flooding
impacts. Isolated thunderstorms with frequent lightning and gusty
winds will also be possible.

By Thursday, a gradual drying trend is expected to begin as moisture
values decrease and mid-level relative humidity lowers compared to
earlier in the week. Even so, sufficient low-level moisture combined
with daytime heating and local sea breeze convergence should still
support scattered afternoon showers, mainly across western and
interior Puerto Rico. Flooding impacts should become more localized,
although urban and small-stream flooding will remain possible where
heavier showers develop. Temperatures throughout the period will
remain warm to hot across coastal areas, with heat indices
occasionally exceeding climatological normal where sunshine is more
persistent.

&&

.Long Term(Friday through next Monday)...
Issued at 317 AM AST Tue Apr 28 2026

By the end of the week, a moist and unstable weather pattern will
persist across Puerto Rico and the U.S. Virgin Islands, accompanied
by a troughing pattern aloft, light to moderate southeasterly winds,
and above-normal moisture across the forecast area. Current guidance
suggests that precipitable water values will remain in the 75th
percentile for this time of year, around 1.80 to 2.00 inches. This
will continue to support a pattern of showers across windward areas
early in the day, followed by active afternoon convection across the
interior, northern, and northwestern portions of Puerto Rico. In
addition, 500 mb temperatures will remain between -7 and -8 degrees
C (near normal but sufficient to support isolated thunderstorm
development), particularly where the strongest activity develops
during the afternoon on Friday. Accordingly, a limited flood threat
will persist on Friday due to the high potential for ponding of
water on roads and in poorly drained areas.

From Saturday into early next week, a gradual drying trend is
anticipated, leading to improving weather conditions. Precipitable
water values will decrease to near-normal levels (around 1.5 inches
or less), while 250 mb heights increase and 500 mb temperatures warm
as ridging builds aloft, bringing greater atmospheric stability.
Although afternoon showers may still develop due to local effects,
their coverage and intensity will be reduced. Any shower activity
during this period should be brief and limited.

Lastly, warm conditions will persist throughout the period as
indicated by temperature guidance at 925 mb which suggests values
will remain above normal through at least next weekend. Also, an
east to southeasterly wind flow will prevail supporting those
conditions. Maximum surface temperatures will range from the upper
80s to low 90s across coastal and urban areas, and from the low to
mid 80s in higher elevations. Combined with high humidity, heat
indices are expected to exceed upper 90s to low 100s degrees F each
day. As a result, a limited heat threat will remain in place for
urban, coastal, and low-elevation areas. Residents and visitors are
encouraged to stay hydrated and avoid prolonged sun exposure during
peak heat hours.

&&

.AVIATION...
(18Z TAFS)
Issued at 222 PM AST Tue Apr 28 2026

Unstable weather conds will continue to produce SHRA/TSRA across
all terminals with brief MVFR/IFR possible. Recent PIREPs rpt
LGT/MOD TURB with MTN OBSC, especially nr TJSJ. TURB may persist
through the evening at terminal sites and En Route as unsettled
weather continues, particularly near areas of strong TS. BKN/OVC
cigs FL015FL060 expected at times. Winds will turn light and vrb
aft 28/22Z.

&&

.MARINE...
Issued at 222 PM AST Tue Apr 28 2026

A series of surface highs and frontal lows over the western to
central Atlantic will continue over the next few days. This will
result in a weaker pressure gradient that will in turn promote
variable, light to gentle southeasterly winds, becoming more east-
northeasterly tonight and then more east-southeasterly again on
Thursday and east to east southeasterly on Friday. Moisture over
the region and a nearby trough will continue to result in showers
and isolated t-storms over the next few days. Pulses of small,
long- period northeasterly swell will continue to spread across
the Atlantic waters and local passages for the next few days,
though seas should remain between 2 to 4 feet.

&&

.BEACH FORECAST...
Issued at 222 PM AST Tue Apr 28 2026

Up to a moderate risk of rip currents will continue over the
region as pulses of a small, long period northeasterly swell
spreads across the local waters and passages with conditions
somewhat improving on Thursday. For tonight and tomorrow, this
moderate risk of rip currents will persist for the northern
coastline of Puerto Rico, and for Culebra and St. Croix, meaning
that life-threatening rip currents are possible in the surf zone.
A low risk of rip currents will continue over other areas,
however, life-threatening rip currents often occur in the vicinity
of groins, jetties, reefs, and piers. Beachgoers should also
continue to monitor the forecast for showers and afternoon
t-storms in the area, especially near northern coastal areas of
Puerto Rico, resulting in heavy rain, lighting and gusty winds.

&&

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

$$

SHORT TERM/AVIATION...CVB
LONG TERM....YZR
MARINE/BEACH FORECAST...MRR

NWS SJU Office Area Forecast Discussion