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998
FXCA62 TJSJ 170650
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
250 AM AST Fri Apr 17 2026

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

.KEY MESSAGES...
Updated at 250 AM AST Fri Apr 17 2026

 * Another active afternoon is forecast today, with some instability
   present and sufficient moisture across the area. Therefore, a
   limited to elevated flooding risk is expected.

 * More stable conditions are expected on Sunday, with drier air
   and warmer Temperatures aloft limiting widespread shower
   activity.Therefore, a typical trade wind pattern will prevail,
   bringing passing morning showers to eastern Puerto Rico and the
   U.S. Virgin Islands, followed by isolated afternoon convection
   over western Puerto Rico.

 * A moderate risk of rip currents will persist across several
   beaches, particularly along exposed coastal areas, creating
   hazardous conditions for swimmers.

 * The U.S.Virgin Islands will experience variable weather conditions
   today, with periods of passing showers, followed by gradual
   improvement into Sunday and continuing into the upcoming
   workweek.

&&

.Short Term(Today through Sunday)...
Issued at 250 AM AST Fri Apr 17 2026

During the overnight hours, weather conditions were variable, with
showers mainly affecting the local waters and some moving across
southeastern sections of the island. As of 2 AM, showers were
brushing the coastal areas of Vieques and St. Croix, with minimal
rainfall accumulations reported. Winds prevailed from the east-
southeast at speeds of 10 mph or less. Temperatures during the
night ranged from the mid to upper 70s along coastal areas, while
cooler conditions were observed across the mountainous regions.

Today, as the upper-level trough amplifies over the western
Atlantic and shifts eastward away from the area, the forecast area
will remain under its divergent side to the southeast, supporting
favorable conditions for vertical development. This pattern is
reinforced by cooler temperatures aloft and relatively moist
conditions through the mid-levels, which will help sustain cloud
development and shower activity. Model guidance continues to
indicate above-normal moisture levels, with precipitable water
remaining elevated compared to climatology. Additionally, mid-
level instability suggests a moderately unstable environment,
allowing deeper convection, particularly during the peak of the
diurnal heating. At the same time, some variability in mid-level
moisture is expected, which may briefly limit coverage at times;
however, overall conditions remain conducive for scattered
showers. The presence of modest low-level flow will aid in
steering activity while maintaining convergence along local
effects and terrain features. Winds are gradually becoming more
easterly. Given these conditions, today will follow a seasonal
pattern, with passing showers across windward areas in the
morning, followed by a more active afternoon driven by diurnal
heating and local effects. Shower activity will concentrate across
the Cordillera Central and northwestern interior, where periods
of moderate to locally heavy rainfall are possible. As a result,
an elevated flooding risk will persist, particularly in urban,
low-lying, and poor drainage areas, where repeated showers could
lead to ponding of water and minor flooding.

By Saturday, a transition toward a drier and more stable pattern
will become more evident across the forecast area. Mid-level
moisture is expected to decrease compared to today, with relative
humidity values lowering across the 700500 mb layer, while
subsidence associated with the shifting upper-level trough will
promote warming aloft and limit vertical development. Although
sufficient low-level moisture will remain to support passing
morning showers, particularly across eastern Puerto Rico and the
U.S. Virgin Islands, overall coverage should be reduced. During
the afternoon, localized convection may still develop across the
western interior of Puerto Rico; however, activity should remain
less organized and shorter-lived due to weaker instability and
reduced lapse rates. Winds will continue from the east to east-
southeast, supporting typical diurnal patterns. As a result,
flooding concerns should diminish compared to today, with only
isolated ponding possible in areas that receive brief, heavier
showers.

On Sunday, similar to Saturday, a stable weather pattern is
expected. Mid-level conditions will remain relatively drier
compared to previous days, with warming aloft promoting increased
stability and limiting vertical cloud development. Although
patches of low-level moisture will continue to move across the
area within the easterly wind flow, overall moisture availability
will remain closer to seasonal levels, reducing the potential for
widespread shower activity. At the surface, a strengthening high
pressure system over the central Atlantic will maintain a steady
easterly to east-southeasterly wind flow, supporting typical trade
wind conditions. This pattern will favor passing showers during
the overnight and morning hours across eastern Puerto Rico and the
U.S. Virgin Islands, followed by localized afternoon convection
across the interior and western sections of Puerto Rico driven
mainly by diurnal heating and local effects; however, activity
should remain limited in coverage and intensity due to the more
stable atmospheric profile. As a result, flooding concerns will
continue to decrease, with only isolated ponding possible in areas
that experience brief, heavier showers, and overall conditions
will resemble a typical seasonal pattern with reduced convective
activity across the region.

&&

.Long Term(Monday through Friday)...
Issued at 250 AM AST Fri Apr 17 2026

he forecast remains on track with no significant changes from the
previous discussion. As the influence of the upper-level trough
weakens and exits the northeastern Caribbean, drier and more stable
conditions are expected to return. A mid-level ridge will build over
the area, bringing a stable air mass aloft. At the surface, a
dominant high pressure system over the central Atlantic will
maintain light to moderate easterly winds through mid-week. During
the first half of the period, precipitable water (PWAT) values will
drop to seasonal normals of approximately 1.50 inches and are
expected to remain within that range for the rest of the workweek.

Local conditions will stay seasonal, with occasional showers moving
into the eastern portions of Puerto Rico, Vieques, Culebra, and the
U.S. Virgin Islands during the morning hours. This will be followed
by afternoon convective activity across the interior and western
portions of Puerto Rico. This afternoon activity could result in
moderate to heavy rainfall and isolated thunderstorms due to the
combination of available moisture, daytime heating, and local
effects. Temperatures at 500 mb are expected to remain within
seasonal values of -6C to -8C; therefore, a thunderstorm or two
cannot be ruled out. Due to previous rainfall, soil saturation, and
elevated river levels, the potential for flooding persists.
Temperatures at 925 mb will remain seasonal through most of the
period, with highs in the low to mid-80s across coastal and urban
areas and the upper 70s to low 80s in the higher mountains.

&&

.AVIATION...
(06Z TAFS)
Issued at 250 AM AST Fri Apr 17 2026

Mainly VFR conditions prevail, with brief MVFR possible in SHRA
over eastern terminals. SHRA brushing TISX are resulting in lower
CIGs.SHRA and isolated TSRA developing during the afternoon over
the interior and western sections, including from 17/18Z to
17/23Z, will result in periods of MVFR conditions with reductions
in VIS. Winds will remain light and variable early, becoming east
to east-southeast at 812 knots after 17/14Z. Gusty winds are
possible near SHRA/TSRA and with sea breeze variations.

&&

.MARINE...
Issued at 250 AM AST Fri Apr 17 2026

A mid-to upper-level trough will maintain an unstable weather
pattern across the regional waters, resulting in periods of strong t-
storms through at least Saturday. A surface high over the western to
central Atlantic will promote moderate to locally fresh east to
southeast winds, in turn resulting in moderate to choppy seas
through at least early next week. A small northeasterly swell will
also continue to propagate across the Atlantic waters and Caribbean
passages through early next week, contributing to hazardous marine
conditions at times.  T-storms can produce locally higher winds,
frequent lightning, and reduced visibility.
&&

.BEACH FORECAST...
Issued at 250 AM AST Fri Apr 17 2026

Up to a moderate risk of rip currents (life-threatening rip currents
are possible in the surf zone) will be in effect through the
weekend, especially along north and east facing beaches of Puerto
Rico and the U.S. Virgin Islands. A long period northerly swell may
arrive by the next midweek, potentially deteriorating coastal
conditions. Beachgoers should remain alert for afternoon showers and
isolated t-storms.

&&

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

$$

SHORT TERM, AVIATION & KEY MESSAGES...LIS
LONG TERM....GRS
MARINE & BEACH FORECAST...MRR

NWS SJU Office Area Forecast Discussion