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619
FXCA62 TJSJ 051901
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
301 PM AST Sun Apr 5 2026

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

.KEY MESSAGES...
Updated at 259 PM AST Sun Apr 5 2026

* Showers and isolated thunderstorms are expected across the
  islands tomorrow, with the potential for locally heavy
  rainfall, especially during the afternoon hours.

* Marine and coastal conditions will gradually improve through
  early this week as the northeasterly swell continues to subside.

* A showery pattern will persist across the region through at least
  midweek due to lingering moisture and the presence of nearby
  troughs.

* Marine and coastal conditions are expected to deteriorate again
  by Wednesday as another northerly swell reaches the region,
  increasing seas and the risk of rip currents.

* Heat indices are forecast to rise above 100F for the first time
  this year, resulting in hot and humid conditions across lower
  elevations.

&&

.Short Term(This evening through Tuesday)...
Issued at 259 PM AST Sun Apr 5 2026

A breezy to locally windy east-southeast wind flow will persist
across the islands to start the short term period. This steering
flow will continue due to a surface high-pressure system building
over the western to central Atlantic that will gradually move
towards the central Atlantic as low pressure systems move over the
western Atlantic. 925 mb wind speeds will gradually decrease to
more normal values as the period progresses. Tonight, showers will
continue to be steered towards windward sectors of the island
while afternoon convection gradually dissipates and/or moves
offshore. Patches of moisture embedded in the ESE flow will
continue to move over the region, leading to passing trade wind
showers primarily affecting the windward sectors during the
overnight and early morning hours. Precipitable water (PWAT)
values will continue at above normal (above 1.75 in) values for
this time of the year throughout most of the short term period as
moisture from the Caribbean will continue to be steered over the
region. Mid-level relative humidity will also continue at normal
to above normal values. Atmospheric instability will be present
due to a mid- to upper-level trough and a jet near the region.
Taking this into account with the above mentioned available
moisture as well as diurnal heating, local sea breeze convergence,
and orographic effects, afternoon convection is forecast each day
as showers and t-storms develop mainly over interior to western-
northwestern PR, and downwind of El Yunque, the USVI, Vieques and
Culebra. This will result in a limited to locally elevated
flooding risk each day as reduced visibility, ponding of water in
roads and poorly drained areas, flooding in urban areas, roads,
small streams, and washes are forecast. Galvez-Davison Index (GDI)
values are around 25 to 30 tomorrow Monday, and higher, 30 to 40
Tuesday, also suggesting the potential for t-storm development.
925 temperatures will be at normal to above normal values under
the ESE flow, prompting a possible limited heat risk particularly
on Tuesday. Showers will continue to reach windward areas during
the morning to overnight hours.

&&

.Long Term(Wednesday through next Saturday)...
Issued at 300 AM AST Sun Apr 5 2026

The current forecast remains on track, with a period of wet and
unstable weather across Puerto Rico and the U.S. Virgin Islands.
This pattern is driven by a mid-to-upper-level trough approaches
from the west and settles over the northeastern Caribbean. At the
surface, an induced inverted trough near Hispaniola will maintain a
persistent southeasterly wind flow, pulling deep tropical moisture
into the region. Precipitable water (PWAT) values are forecast to
reach 2.00 to 2.20 inches by Wednesday, well above climatological
normals.

Combined with above-normal temperatures at the 925 mb level, this
setup could drive heat indices into the low 100s for the first time
this year, a trend that may persist through the weekend.
Furthermore, cooler mid-level temperatures ranging from -8C to -9C
will likely enhance convective instability, leading to intense
thunderstorms and frequent lightning.

Daily widespread rainfall and thunderstorms are anticipated,
particularly during the afternoon hours across central, northern,
and northwestern Puerto Rico, including the San Juan metro area.
This activity will be enhanced by diurnal heating and local effects.
The most active period is expected on Wednesday and Thursday,
bringing a high risk of: heavy rainfall, gusty winds, frequent
lightning, rapid river rises, potential landslides and urban and
small stream flooding, especially in areas with saturated soil. In
contrast, the U.S. Virgin Islands will likely experience only
occasional passing showers with minor impacts during this timeframe.

Conditions are expected to improve by Friday as the trough weakens
and departs the area. While lingering moisture may trigger isolated
or scattered showers, the overall intensity and coverage will
diminish. From Saturday onwards, the region will transition back to
a more stable weather pattern, characterized by passing trade wind
showers and typical afternoon convection over central and western
Puerto Rico.

&&

.AVIATION...
(18Z TAFS)
Issued at 259 PM AST Sun Apr 5 2026

Mainly VFR conditions with possibly brief MVFR for TJBQ and TJSJ.
ESE flow will continue at 10 to 20 kts with higher gusts,
especially near SHRA. -SHRA/VCTS can continue to develop over the
interior and steered northward. Winds decreasing after 05/23Z,
locally higher near -SHRA/VCSH that will be steered towards
windward sectors, and increasing again from the ESE at 10 to 20
kts with higher gusts at 06/13Z.

&&

.MARINE...
Issued at 259 PM AST Sun Apr 5 2026

Hazardous marine conditions are expected to persist through at least
Monday afternoon into the evening. The primary drivers of these
conditions include a strong high-pressure system over the Atlantic,
which will maintain moderate to fresh southeasterly winds through at
least midweek. As a result, winds will remain moderate to choppy
across the local waters. In combination with a fading northeasterly
swell, seas will remain choppy to rough, particularly across the
Atlantic waters and local passages tonight and on Monday. Improving
marine conditions are forecast beginning Tuesday, with seas
subsiding to around 5 feet across the Atlantic waters and up to 4
feet across the Caribbean waters.

While trade wind showers continue across the region, isolated to
scattered thunderstorms are expected, especially during the
afternoon hours over coastal waters, particularly near western and
northwestern Puerto Rico. Shower and thunderstorm coverage may
increase slightly throughout the week as a series of nearby troughs
interact with abundant tropical moisture.

&&

.BEACH FORECAST...
Issued at 259 PM AST Sun Apr 5 2026

A high risk of rip currents will continue across the northern and
eastern coasts of Puerto Rico, including Vieques, Culebra, and the
U.S. Virgin Islands, where life-threatening conditions are present.
Breaking waves may still reach up to 7 feet along the northern
coastline due to a fading northeasterly swell and breezy conditions.
Therefore, a high risk of rip current is in effect until Monday
afternoon. A gradual improvement is forecast from Monday evening
into Tuesday, with a moderate risk before conditions potentially
deteriorate again by midweek as another swell arrives. Beachgoers,
especially inexperienced swimmers, are strongly urged to stay out of
the water, avoid areas near rocks or jetties, and follow all posted
warnings and lifeguard guidance. Additionally, passing showers and
isolated thunderstorms may develop, particularly in the afternoon,
producing gusty winds and brief heavy rainfall; seek shelter if
thunder is heard. For additional information and location-specific
rip current details, please visit: weather.gov/beach/sju.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Monday afternoon for PRZ001-002-
     005-008-012.

     High Rip Current Risk through late tonight for PRZ010-013.

VI...High Rip Current Risk through Monday afternoon for VIZ002.

     High Rip Current Risk through late tonight for VIZ001.

AM...Small Craft Advisory until 6 PM AST Monday for AMZ711.

     Small Craft Advisory until 6 AM AST Monday for AMZ712-716-741.

     Small Craft Advisory until noon AST Monday for AMZ723.

&&

$$

SHORT TERM/AVIATION...MRR
LONG TERM...GRS
MARINE/BEACH FORECAST...LIS

NWS SJU Office Area Forecast Discussion