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355
FXCA62 TJSJ 151755
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
155 PM AST Thu Oct 15 2026

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

.KEY MESSAGES...
Issued at 130 PM AST Thu Oct 15 2026

- Showers and isolated thunderstorms will affect interior,
  western,and southwestern Puerto Rico today, potentially causing
  localized urban and small-stream flooding. Drier conditions are
  expected Friday through early next week.

- Expect, brief passing showers, especially during the overnight
  and morning hours across the US Virgin Islands. A more active
  weather pattern may develop by midweek as moisture increases and
  winds weaken.

- Elevated heat indices will pose a risk through the weekend,
  particularly for outdoor workers and vulnerable populations.
  Stay hydrated, limit strenuous outdoor activities, and take
  frequent breaks in shaded or air-conditioned areas.

- Moderate rip currents across northern, western, eastern beaches
  of Puerto Rico, spreading to more areas during the weekend.
  Mariners and beachgoers should monitor the latest marine
  conditions.

&&

.Short Term(This evening through Saturday)...
Issued at 130 PM AST Thu Oct 15 2026

A transition to a drier and more stable atmospheric pattern will
unfold across the local islands through Saturday. Recent satellite
precipitable water imagery shows drier air advancing into the
northeastern Caribbean. However, today`s 12z SJU upper-air sounding
indicates abundant low-level moisture, with precipitable water
(PWAT) around 1.88 inches and surface-based CAPE exceeding 2000
J/kg, but also shows a trade-wind cap near 850 mb and dry air above
700 mb. Low-level easterly trade winds of 12 to 19 knots, combined
with daytime heating and local sea breeze convergence, will trigger
scattered to numerous showers and isolated thunderstorms mainly over
the interior, western, and southwestern sections of Puerto Rico.
Localized rainfall totals of 1.50 to 2.50 inches could produce urban
and small-stream flooding and ponding on roads across those areas.
Across the U.S. Virgin Islands, streamers are expected to develop
downwind of the islands, with brief periods of light showers over
land. However, passing trade wind showers under an advective pattern
will return tonight into Friday morning across the USVI and
east/northeast sections of PR.

Under a building mid-to upper-level ridge, model guidance shows PWAT
falling from near 1.90 inches today to around 1.50 inches by Friday
afternoon, near the 25th percentile for mid-October. Mid-level
temperatures will remain warm between -4C and -5C, causing weak
lapse rates and persistent subsidence that will cap vertical
convective growth after today. Therefore, on Friday and Saturday,
convection will become increasingly limited to scattered showers and
isolated thunderstorms over western PR. Meanwhile, fair weather
conditions prevail across eastern PR and the USVI, with mostly
passing morning showers.

Elevated boundary-layer temperatures will sustain heat hazards
across the islands through the weekend. Model guidance indicates 925
mb temperatures peaking between 22.5-23.5C, near the upper end of
the 75th percentile climatology. Combined with typical warm-season
dew points, afternoon heat indices are forecast to reach 102F to
107F, with higher values in isolated areas across the northern,
western, and southern coastal plains, posing heat risks to outdoor
workers and vulnerable populations.

&&

.Long Term(Sunday through next Wednesday)...
Issued at 130 PM AST Thu Oct 15 2026

The long-term forecast remains on track, with primarily stable
weather conditions expected Sunday through early next week, followed
by more active afternoons and slow-moving showers and thunderstorms
by midweek.

A mid-to upper-level ridge will maintain dry and stable conditions
aloft through Tuesday. Precipitable water (PWAT) will remain below-
seasonal levels, ranging from 1.5 to 1.7 inches. Easterly steering
winds will persist as low-level surface high pressure and a frontal
boundary remain north of the local area. Passing cloud patches and
trade wind showers will reach eastern sections of the islands
(including the U.S. Virgin Islands) from time to time, with no
significant impacts. Diurnal heating and local effects will still
favor the development of afternoon showers and isolated
thunderstorms across the interior to western sections of Puerto
Rico, as well as downwind from El Yunque toward the southern half of
the San Juan metropolitan area, and downwind from the USVI, Vieques,
and Culebra. A limited flood threat will remain present each
afternoon across interior to western Puerto Rico.

By the end of the day on Tuesday, the mid-level ridge will gradually
dissipate. In its place, a mid-to-upper level trough will begin to
cool the mid-levels and bring the lapse rates up to seasonal values,
potentially enhancing the development of deep convection by
Wednesday into Thursday. The steering flow will also experience a
gradual weakening, especially by Wednesday, as the interaction
between a surface-level trough and ridge to the north of the CWA
leads to the collapse of the winds down to approximately 5 kts. By
Tuesday, the direction of the steering flow will gradually shift to
be from E to SE into the afternoon. This SE to S pattern will
persist into the remainder of the long term period. The precipitable
water values and column relative humidity will range between below
to around seasonal levels on Tuesday and Wednesday and gradually
increase into the afternoon on Thursday. The convective activity
that develops each day will thus be driven by local effects,
available moisture, and steering flow strength and direction.
Rainfall may be expected to develop each day across the CWA and
particularly affect the northern interior, interior, northwest, and
northeast sectors of Puerto Rico. Advective showers may also develop
and impact portions of the US Virgin Islands and southeastern Puerto
Rico during the mornings and overnight hours.

A limited heat threat remains favored throughout the long-term
period. While widespread heat hazards are not anticipated, extremely
sensitive individuals could be affected and should take appropriate
precautions to protect themselves from heat-related stress.

&&

.AVIATION...
(18Z TAFS)
Issued at 130 PM AST Thu Oct 15 2026

Mainly VFR conditions will prevail across all terminals during the
next 24 hours. However, locally induced afternoon TSRA over central
PR may cause tempo MVFR conds at TJPS til 15/22z. VCTS possible
across the rest of the PR terminals thru 15/22z. The 15/12z TJSJ
sounding indicated east winds up to 19 kt blo FL030, light winds
with a northeasterly component expected overnight.

&&

.MARINE...
Issued at 130 PM AST Thu Oct 15 2026

Generally favorable marine conditions are expected through the end
of the workweek, with light to moderate easterly winds and
relatively tranquil seas. However, afternoon showers and isolated
thunderstorms may produce locally hazardous conditions, particularly
across the western and coastal waters of Puerto Rico. A lingering
northeasterly swell will gradually subside through Friday, followed
by another long-period northeasterly swell arriving during the
weekend, resulting in increasing seas across the Atlantic waters.

&&

.BEACH FORECAST...
Issued at 130 PM AST Thu Oct 15 2026

A moderate risk of rip currents will continue along the beaches
of San Juan and vicinity, north-central Puerto Rico, and Culebra,
with a low risk elsewhere, including the U.S. Virgin Islands. The
risk will decrease to low across all beaches Friday before
potentially increasing again over the weekend as another long-
period northeasterly swell reaches the region. Afternoon showers
and isolated thunderstorms may also pose a lightning threat to
beachgoers, particularly across western and southwestern Puerto
Rico, with improving conditions expected Friday.

&&

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

$$

SHORT TERM/AVIATION...DSR
LONG TERM...KML
MARINE/BEACH FORECAST...MMC

NWS SJU Office Area Forecast Discussion