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856
FXCA62 TJSJ 041807
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
207 PM AST Sat Apr 4 2026

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

.KEY MESSAGES...
Updated at 207 PM AST Sat Apr 4 2026

* Above-normal moisture and increasing instability will support
  periods of heavy rainfall through midweek.

* Up to an elevated flooding risk will continue, especially across
  windward areas overnight and during the afternoon,
  interior/western/north-western Puerto Rico as well as downwind
  of El Yunque (towards the metro area) and mainly downwind of the
  local islands.

* Breezy to locally windy ESE flow and a fading northeasterly
  swell will persist through early next week, leading to hazardous
  marine conditions for small craft and a high risk of life-
  threatening rip currents along northern and eastern beaches.

* Warmer-than-normal temperatures will develop by midweek, with
  heat indices potentially reaching the low 100s by mid next week.

&&

.Short Term(This evening through Monday)...
Issued at 207 PM AST Sat Apr 4 2026

In the morning hours, cloudiness and upper cloudiness prevailed
across the local islands. At the local waters, the presence of
pockets of showers was noted by the Doppler Radar, with some of them
streaking along the northern coast of Puerto Rico. Surface winds
prevailed from the east, slightly veering to the east-southeast. As
of 11 AM, Doppler Radar showed the development of shower activity
along the northeastern PR sections, extending into the San Juan
Metropolitan area, due to available moisture and local and diurnal
effects. The shower activity quickly spread along the Cordillera
Central, moving into the western interior, affecting the vicinity of
Mayaguez. According to radar rainfall estimates, accumulations
ranged from 2 to 3 inches across municipalities between Bayamon and
Trujillo Alta, as well as in the western interior. Daytime
temperatures rise due to the lack of deep cloudiness, with
thermometers along the coast reading 84 to 87, and across the
mountains in the low 80s.

For the rest of the day, the broad surface high pressure extending
from the central Atlantic into the Caribbean will dominate the
surface pattern, promoting an east-southeasterly wind flow across
the region. Under this setup, an unsettled weather regime will
persist with the influence of a shortwave trough around 700 mb and a
strong jet streak at 250 mb exceeding 100 knots. This upper-level
support will enhance divergence aloft and promote rising motion
across the islands. As a result, shower activity will be scattered,
with the main focus across the interior to northwestern Puerto Rico
for the rest of the afternoon. Thunderstorm activity is expected
with the remaining strong showers and extending into the western
coastal local waters. Therefore, periods of moderate rainfall may
lead to ponding on roads and reduced visibility, though widespread
flooding is not expected. For tonight, High-Resolution models
suggest an increase in shower activity along windward sections of
Puerto Rico and the U.S. Virgin Islands. This activity is forecast
to be between light and moderate.

On Sunday, the surface high pressure will continue to dominate,
maintaining an east-southeasterly wind flow while a tightening
pressure gradient supports breezy conditions. South winds at 700 mb
will enhance moisture transport across the islands, and an increase
in relative humidity between the 750500 mb layer will support
deeper moisture availability and more efficient cloud development.
This setup, combined with precipitable water values in the 75th
percentile and the lingering influence of an upper-level jet streak
near 70 knots, will favor more persistent and organized shower
activity. Expect increased vertical convergence leading to periods
of steady rainfall, particularly across eastern and southern Puerto
Rico during the morning, shifting toward the interior and
northwestern municipalities by the afternoon. By Monday, the surface
pattern will evolve as the high pressure combines with a surface
disturbance just north of Hispaniola, resulting in a more pronounced
southerly wind flow between 850 and 700 MB. Along with westerly
winds at 500 mb and a 250 mb jet streak near 60 knots, this will
continue to support an active weather pattern. Shower activity will
mainly develop across the interior and northern sections of Puerto
Rico due to local effects and moisture convergence. However, despite
the available moisture, the Galvez-Davison Index (GDI) suggests a
lower potential for thunderstorm development. Periods of moderate
rainfall may still lead to urban and small stream flooding,
particularly in areas experiencing repeated showers.

&&

.Long Term(Tuesday through next Friday)...
Issued at 318 AM AST Sat Apr 4 2026

A wet and unstable pattern will prevail across the region through
much of the long-term period, as a mid- to upper-level trough
approaches from the west and settles across the northeastern
Caribbean. At the surface, an induced inverted trough near
Hispaniola will maintain a persistent southeasterly wind flow across
the region. This will promote the advection of abundant tropical
moisture into the forecast area, with precipitable water (PWAT)
values increasing to near or above 2.0 inches and moisture deepening
through the entire column. This southeasterly flow will also support
above normal temperatures, with model guidance indicating 925 mb
temperatures increasing to near two standard deviations above
climatological normals by midweek. As a result, warmer-than-normal
conditions are expected at the surface, with heat indices
potentially reaching the low 100s for the first time this year in
some areas. In addition to the heat impacts, the increased low-level
warmth will contribute to greater instability, providing additional
fuel for convective development.

Aloft, the presence of the upper-level trough will further enhance
instability, with low- to mid-level lapse rates becoming modestly
steep for the region. Combined with elevated relative humidity
values through the 850-500 mb layer, this will support the
development of heavy showers and widespread convective development.
Under this pattern, scattered to numerous showers and thunderstorms
are expected each day, with activity becoming more widespread during
the afternoon hours due to diurnal heating and local effects. The
most active period is anticipated Wednesday through Thursday, when
the combination of peak moisture, anomalous warmth, and upper-level
support will maximize convective coverage. Thunderstorms during this
period will be capable of producing heavy rainfall, frequent
lightning, and gusty winds. The available heat and instability may
also support stronger thunderstorm development, with the potential
for intense downpours.

As a result, the risk of urban and small stream flooding will remain
elevated, along with the potential for rapid river rises. Saturated
soils and elevated streamflows from previous rainfall will further
exacerbate flooding impacts, particularly across flood-prone and
poor drainage areas.

By Friday onwards, conditions are expected to gradually improve as
the upper-level trough weakens and shifts away from the region.
Although lingering moisture will continue to support isolated to
scattered shower activity, a reduction in overall coverage and
intensity is expected, with a transition toward more typical trade
wind conditions by late in the period.

&&

.AVIATION...
(18Z TAFS)
Issued at 207 PM AST Sat Apr 4 2026

Mostly VFR conditions will persist with some brief periods of MVFR
to IFR for TJPS, TJSJ & TJPS during the TAF period. SFC winds will
continue from the E-SE winds up to 15 knots with gusty winds near
showers. At 04/18Z, SHRA and TSRA will develop across the mountains
and move across TJSJ & TJBQ from 04/18Z-0423Z. This pattern will
allow a temporary change in SFC winds, lower VIS, and lower CIGS in
the FL020 to FL050. winds will diminish at 05/00Z, becoming lighter
up to 8 knots with land breeze variation.

&&

.MARINE...
Issued at 207 PM AST Sat Apr 4 2026

Hazardous marine conditions are expected to persist through early
next week. A strong high-pressure system in the Atlantic will
maintain fresh to locally strong easterly winds today, veering to
become east-southeasterly late this afternoon through most of the
period. When combined with a fading northeasterly swell, seas will
remain choppy to rough, particularly across Atlantic waters and
local passages. While trade wind showers continue across the region,
expect isolated to scattered thunderstorms, especially during the
afternoon hours over coastal waters, especially near western and
northwestern Puerto Rico. Coverage may increase slightly over the
weekend as an upper-level trough arrives, interacting with abundant
tropical moisture.

&&

.BEACH FORECAST...
Issued at 207 PM AST Sat Apr 4 2026

A High Risk of Rip Currents (life-threatening rip currents are
likely in the surf zone) is in effect for the northern and eastern
coastlines of Puerto Rico, Vieques, Culebra and the USVI through
the rest of the weekend. Breaking waves can reach 6 to 9 feet,
particularly over the northern coastline of Puerto Rico. This is
due to a subsiding northeasterly swell and breezy to locally windy
condtions.

Although hazards will gradually subside, a high rip current risk
will persist for most of these areas through Monday. Beachgoers
and inexperienced surfers are strongly urged to stay out of the
water. Up to a moderate risk of rip currents is forecast Tuesday
and Wednesday, before increasing to high again by Thursday.

Beachgoers and inexperienced surfers are urged to avoid going
into the water, walking over rocks or jetties, as life-
threatening rip currents are very likely. Heed the advice of
lifeguards, beach patrol flags, and signs. Access to hazardous
beaches may be limited, and individuals should follow all posted
warnings and safety guidance.

Visitors should also be mindful of the weather, in addition to
surf hazards. In addition to the life- threatening rip currents,
beachgoers should stay weather alert due to isolated showers and
thunderstorms capable to produce gusty winds, periods of heavy
showers, and lightning. If thunder is heard, immediately seek
refuge inside a sturdy building.


&&

.HYDROLOGY...
Issued at 318 AM AST Sat Apr 4 2026

Hydrologic conditions will become increasingly favorable for
flooding impacts through much of the forecast period. Elevated
moisture (PWAT 2.0 inches), increasing instability, and efficient
warm-rain processes will support periods of heavy rainfall.

Flooding is not expected to be widespread; however, there is an
elevated risk of urban and small stream flooding, especially in
areas experiencing repeated or slow-moving showers. The highest
risk will occur overnight across windward areas and during the
afternoon across interior and western Puerto Rico.

Recent rainfall has resulted in saturated soils across portions
of eastern and northern Puerto Rico, increasing runoff efficiency
and the likelihood of rapid rises in streams and rivers,
particularly in steep terrain.

The flooding risk is expected to increase from this afternoon
through midweek, with the potential for isolated flash flooding,
especially during the peak period from Wednesday through Thursday.

Conditions should gradually improve late in the week as moisture
decreases and instability weakens.

&&

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

     High Rip Current Risk through late Sunday night for PRZ010-013.

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

     High Rip Current Risk through late Sunday night for VIZ001.

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

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

     Small Craft Advisory until noon AST Monday for AMZ723.

     Small Craft Advisory until 6 PM AST Sunday for AMZ741.

     Small Craft Advisory until noon AST Sunday for AMZ742.

&&

$$

SHORT TERM/AVIATION...LIS
LONG TERM...CVB
MARINE/BEACH FORECAST...MRR
HYDROLOGY...CAM

NWS SJU Office Area Forecast Discussion