819
FXCA62 TJSJ 100858
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
457 AM AST Fri Apr 10 2026

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

.KEY MESSAGES...
Updated at 557 AM AST Fri Apr 10 2026

* A High Risk of Rip Currents is in effect for the northern coast of
  Puerto Rico and Culebra through the weekend due to a long-period,
  northwest to northerly swell.

* Generally stable weather is forecast through Saturday, with
  isolated showers over windward areas and afternoon convection over
  mainly interior to W-NW PR.

* An approaching mid to upper level trough will result in a wetter
  and more unstable pattern with an increased flooding risk as it
  reaches the islands late Sunday into the next workweek.

 * A limited heat threat will be present today and tomorrow,
   mainly in coastal and urban areas.

&&

.Short Term(Today through Sunday)...
Issued at 557 AM AST Fri Apr 10 2026

Since midnight, radar estimated rainfall accumulations showed
minimal amounts over eastern PR, Vieques and then northern USVI. The
strongest observed shower/t-storm remained over the western offshore
Atlantic waters. Official and unofficial stations reported minimum
temperatures in the 70s across coastal areas, with some isolated
stations reporting 78 to 80 degrees, and in the 60s across interior
PR.

Current satellite derived precipitable water (PWAT) values indicate
a band of moisture that arrived during the overnight hours and
promoted the above mentioned showers, with values up to 1.65 in
(at normal values for this time of the year). A broad surface high
over the central Atlantic interacting with a frontal low over the
western Atlantic, and then another building high over the western
Atlantic to end the short term period will continue to result in
E to ESE steering flow. 925 wind speeds are forecast to continue
up to around 15 kts, normal for this time of the year. Today,
Friday, is forecast to be the driest day in the short term period.
E to ESE steering flow will steer patches of moisture and drier
air towards the area. Satellite imagery already detects the patch
of drier air (PWAT values below 1.5 in) that will move over the
islands later today and is forecast to be over western PR by this
afternoon, serving to limit afternoon convection. Afternoon
showers are still forecast over mainly interior to W-NW PR due to
diurnal heating, local orographic effects and sea breeze
convergence. Showers will also continue to reach windward sectors
of the islands. 500 mb temperatures, 250 mb heights, 700 to 500 mb
relative humidities will be at normal values, promoting stability
and inhibiting shower and t- storm development. Moisture will
continue to be steered towards the islands during the period. PWAT
values will increase to high end normal to above normal values
(above 1.75 in) on Saturday and Sunday while 500 mb temperatures
cool and 250 mb heights decrease.

For tomorrow, Saturday, an enhanced pattern will be present with
a limited flooding risk forecast during the afternoon over W-NW PR
due to convective showers and t-storms. Showers can also develop
downwind of the local islands. Advective showers will also
continue to reach windward sectors of the islands during the
morning and overnight hours. A mid to upper level trough is
forecast to approach the region from the E/NE on Sunday, reaching
the islands late Sunday into Monday. This will make Sunday a
transition day toward a wetter and more unstable pattern forecast
during the long term period. This will result in an increase in
shower frequency over windward sectors during the morning and
enhanced afternoon showers and t-storms, a limited flooding risk
will persist to end the weekend but can be increased to an
enhanced flooding risk. Showers and isolated t- storms can also
reach windward sectors Sunday night and into the long term period.
Galvez- Davison Index (GDI) values are forecast at up to 15
today, up to 30 to 35 on Saturday and up to 40 on Sunday. For
additional details, including rainfall expectations and hydrologic
conditions Sunday onwards, refer to the Hydrologic Outlook
(ESFSJU). Patchy fog over will be present during the overnight
hours over areas of the interior. Satellite and model guidance
also suggest low concentrations of Saharan Dust persisting through
the short term period. 925 mb temperatures are forecast to be
warmer than normal, with highs reaching the upper 80s to around 90
at urban and coastal areas. A limited heat risk will persist,
today and Saturday.

&&

.Long Term(Monday through Friday)...
Issued at 557 AM AST Fri Apr 10 2026

A wetter and more unstable pattern will develop Monday and persist
through midweek as a deep-layered trough and developing upper-level
low remain northwest of the region, supporting favorable divergence
aloft through at least Tuesday night. Deep moisture will surge into
the area from the east on Monday, with precipitable water values
exceeding climatological maxima before organizing into a moisture
band that lingers over the region Tuesday into Wednesday, then
gradually shifts southwestward into the Caribbean by Thursday. Low-
level winds will veer from EENE Monday to ESE by midweek,
supporting a transition from a more typical diurnal pattern early
Monday to increasingly widespread and organized convection Monday
afternoon through at least Tuesday, and possibly into Wednesday.
Cooler temperatures aloft through Tuesday night will enhance
instability, followed by gradual warming by Wednesday into Thursday,
leading to a slow decrease in convective intensity, although a moist
column will persist.

The primary concern is an elevated to locally significant flooding
risk, increasing Monday afternoon and peaking Tuesday into
Wednesday. Periods of heavy and repeated rainfall may result in
urban and small stream flooding, isolated flash flooding, and
localized landslides or rapid river rises. Slower storm motion,
particularly on Tuesday, could enhance rainfall totals in affected
areas. Model guidance has been consistent in highlighting this
event, including the ECMWF Extreme Forecast Index, which indicates
anomalously high rainfall potential building Monday, peaking Tuesday
into Wednesday, and diminishing by Thursday. Although activity
should become less organized late in the period, above-normal
moisture will continue to support scattered showers with localized
impacts. Confidence is moderate to locally high in the overall
pattern, though some uncertainty remains in the exact placement of
the heaviest rainfall.

For additional details, including rainfall expectations and
hydrologic conditions, refer to the Hydrologic Outlook (ESFSJU).

&&

.AVIATION...
(06Z TAFS)
Issued at 557 AM AST Fri Apr 10 2026

Mainly VFR conditions. E to ESE, at times, light and variable winds
to up to 11 kts through 10/13Z, then increasing to around 15 kts
with higher gusts and seas breeze variations. VCSH/-SHRA over
eastern terminals through the period. SHRA then near or at JBQ at
10/17-22Z. Winds decreasing again after 10/23z.

&&

.MARINE...
Issued at 557 AM AST Fri Apr 10 2026

Winds will turn more easterly from today and through the weekend as
a broad surface high pressure builds from the Central Atlantic. A 4
to 5 feet northwest to north swell will spread across the Atlantic
waters and passages, building seas up to 6 feet for the next few
days. Therefore, small craft should continue to exercise caution,
mainly over the Atlantic Waters. Another pulse of the northerly
swell is expected on Sunday. By early next week, a frontal boundary
and a pre- frontal trough will increase showers and thunderstorms
across the regional waters. Increasing winds and seas building up to
7 feet are also expected, and Small Craft Advisories could be issued
for the Atlantic waters during this period.

&&

.BEACH FORECAST...
Issued at 557 AM AST Fri Apr 10 2026

A 4 to 5 feet long-period, northwest to northerly swell will
gradually spread across the Atlantic waters and passages today. This
will keep an elevated threat of life-threatening rip currents along
the Atlantic beaches of Puerto Rico and Culebra, where a High Rip
Current Risk remains in effect through the weekend. By early
Sunday, another pulse from the northerly swell is expected to
reach the northern exposed coastal waters. Across the USVI,
Vieques, and the south facing beaches of PR, up to a moderate
risk of rip currents is expected to prevail through the same
period.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Sunday afternoon for PRZ001-002-
     005-008.

     High Rip Current Risk through Saturday afternoon for PRZ012.

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

$$

SHORT TERM/AVIATION...MRR
LONG TERM....ICP
MARINE/BEACH...DSR

NWS SJU Office Area Forecast Discussion