National Weather Service Today's Weather Impact Levels

425
FXCA62 TJSJ 040718
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
318 AM AST Sat Apr 4 2026

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

.KEY MESSAGES...
Updated at 318 AM AST Sat Apr 4 2026

* Breezy to locally windy conditions and a fading northeasterly
  swell will persist through early next week, leading to hazardous
  marine conditions and the formation of life-threatening rip
  current along northern and eastern beaches.

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

* Elevated flooding risk, especially across windward areas
  overnight and interior/western Puerto Rico each afternoon.

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

&&

.Short Term(Today through Monday)...
Issued at 318 AM AST Sat Apr 4 2026

Fair weather prevailed today across the islands, with passing
showers across the local waters and moving inland across the
windward sections in PR and the USVI occasionally. The easterly
winds were mainly 10 or less, with land-breeze variations,
especially along the leeward sections. Most coastal and urban
sites recorded minimum temperatures in the low or mid-70s, while
mountain sites recorded maximum temperatures in the low 60s.

A surface high-pressure system over the central Atlantic will
maintain an east to southeast wind flow across Puerto Rico and the
U.S. Virgin Islands. This will result in breezy to locally windy
conditions, with low-level winds generally between 15 and 20
knots. Under this surface regime, moisture levels will remain near
or above climatological normal (with precipitable water (PWAT)
values ranging from 2.0 to 2.2 inches, near or above the 75th
percentile), supporting the development of trade wind showers.
These showers will primarily affect windward locations each day,
especially during the overnight and early morning hours, from late
tonight into Sunday, and again from Sunday night into early
Monday.

A mid- to upper-level trough will gradually increase instability,
with 700-500 mb lapse rates approaching 6.0-6.5 C/km. Combined
with mid-level humidity between 70 and 90 percent, this
environment will support efficient rainfall processes with some
isolated thunderstorms between the afternoon and evening hours. By
Sunday into Monday, this trough is expected to extend into the
upper levels across or near the northeastern Caribbean, further
enhancing atmospheric instability across Puerto Rico and the U.S.
Virgin Islands.

This evolving pattern will favor periods of trade wind showers
during the overnight and morning hours, particularly across
windward areas. When combined with low-level convergence, these
showers could produce locally heavy rainfall and increase the risk
of flooding in these regions. During the afternoon and evening
hours, strong convective development is expected across interior
and western Puerto Rico, with additional impacts possible across
eastern Puerto Rico and the U.S. Virgin Islands.

Overall, this pattern supports an elevated risk of flooding
rainfall in the short term. Beach forecast

Confused seas are creating life-threatening rip currents along
north-facing beaches of Puerto Rico and the U.S. Virgin Islands,
where entering the water is strongly discouraged. While south-
facing beaches have a lower risk, caution is still advised as
conditions can change quickly.

&&

.Long Term(Tuesday through Saturday)...
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...
(06Z TAFS)
Issued at 318 AM AST Sat Apr 4 2026

Mainly VFR conditions expected, with brief MVFR/IFR conditions
possible in SHRA/TSRA. Trade wind showers will impact eastern
terminals overnight, while afternoon convection (04/16-23z) may
affect interior and western Puerto Rico as well as windward
terminals, including TJBQ and TJSJ. Expect calm to light and VRB
winds thru 04/13z, then winds from the east to southeast at 10-16
kt with higher gusts. Mountain obscurations likely during periods
of heavier showers and TSRA.

&&

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

Hazardous marine conditions are expected to persist through next
week. A strong high-pressure system in the Atlantic will maintain
fresh to locally strong easterly winds today, veering east-southeast
late this afternoon through Sunday. When combined with a subsiding
northeasterly swell, seas will remain choppy to rough, particularly
across Atlantic waters and local passages. Consequently, Small Craft
Advisories remain in effect for the Atlantic offshore and coastal
waters, including the Anegada and Mona Passages through Sunday
afternoon. While trade wind showers continue across the region,
expect isolated to scattered thunderstorms 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 318 AM AST Sat Apr 4 2026

Beaches across northern and eastern Puerto Rico, including Vieques,
Culebra, and the U.S. Virgin Islands will remain hazardous for
beachgoers throughout the weekend and into early next week. A
subsiding northeasterly swell continues to spread across Atlantic
waters and passages, with breezy to locally windy conditions along
the coasts. Given these conditions, a High Rip Current Risk remains
in effect for northern and eastern beaches of the islands through
Sunday afternoon. Beachgoers and inexperienced surfers are strongly
urged to avoid entering the water or walking on rocks and jetties,
as life-threatening rip currents are highly likely. Always heed the
advice of lifeguards and pay close attention to beach patrol flags
and signs.

&&

.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 Sunday afternoon for PRZ001-002-
     005-008-010-012-013.

VI...High Rip Current Risk through Sunday afternoon for VIZ001-002.

AM...Small Craft Advisory until 6 PM AST Sunday for AMZ711-712-716-
     723-741.

     Small Craft Advisory until noon AST Sunday for AMZ742.

&&

$$

KEY MESSAGES/SHORT TERM/AVIATION/HYDROLOGY...CAM
LONG TERM....CVB
MARINE/BEACH FORECAST/GRS
AVIATION...GRS

NWS SJU Office Area Forecast Discussion