Qtas De Valle Verde, Puerto Rico Weather Forecast Discussion

550
FXCA62 TJSJ 251821
AFDSJU
Area Forecast Discussion
National Weather Service San Juan PR
221 PM AST Thu Sep 25 2025
.KEY MESSAGES...
* Conditions will slowly improve from now on. However, periods of
  showers and thunderstorms remain possible due to the proximity
  of the tropical wave (AL94). A few rounds of heavy rainfall
  could still produce localized flooding.
* Through Friday morning: another round of showers and
  thunderstorms is likely, particularly over the west and southern
  PR, with isolated higher rainfall totals possible.
* For the US Virgin Islands, conditions are expected to continue
  improving from now onward; however, a few periods of showers and
  thunderstorms cannot be ruled out, especially through early
  Friday morning.
* As Humberto moves along the NHC track over the Atlantic, at a
  safe distance from PR and the USVI, it creates uncertainty in
  the forecast. Conditions may become unstable and moist by next
  Monday.
&&
.SHORT TERM...Tonight through Saturday...
As Tropical Wave (AL94) moves away from PR and the USVI, a line
with strong thunderstorms moved across southwest PR, producing
downpours over Cabo Rojo, Lajas, and Guanica, where urban and
small stream flooding were reported. Maximum temperatures were in
the low 90s along Vieques, Culebra, and the US Virgin Islands, and
in the upper 80s across the northeastern part of PR.
Although weather conditions are expected to improve for some
locations in PR and the USVI, showers and thunderstorms cannot be
ruled out, which may impact the western and southwestern parts of
PR, as well as the northeast quadrant. The east-northeast winds
resulting from distant Humberto will bring one or two showers
across the USVI. This weather pattern, combined with saturated
soils, will continue to pose the following hazards and impacts:
localized flooding in flood-prone and low-lying areas, as well as
mudslides or landslides along steep terrain.
As AL94 moves away from the islands, model guidance suggests the
impact of the trailing bands of showers and thunderstorms moving
over PR from the Mona Passage and Caribbean Sea late this
afternoon into the evening. Thus, possible rounds of showers will
remain possible for some areas in PR overnight into early Friday
morning. A seasonal pattern will return from Friday morning
through Saturday.
.LONG TERM...Sunday through Thursday....from the previous
discussion
From Sunday (September 30) through early Tuesday, the local
weather pattern across Puerto Rico and the U.S. Virgin Islands
will be influenced by two tropical systems situated over the
Atlantic. The combination of these two systems will maintain a
southeasterly wind flow across the islands. On Sunday, both global
model guidance (GFS & ECMWF) show a less wet area moving into the
region, with precipitable water values dropping to around 1.70
inches (near the 25th percentile). This brief window of reduced
moisture presence will rapidly end as Hurricane Humberto
progresses farther into the western Atlantic, leading to an
increase in tropical moisture and the tail of the tropical system
over the islands by Tuesday and into early Wednesday. During this
period, mid-level lapse rates between 700 and 500 mb will support
stable conditions aloft due to an upper-level ridge. Thus,
although moisture levels increase, instability will be limited,
and afternoon convection on Tuesday will be driven primarily by
local effects. The bulk of the showers is forecast for the
interior and northwestern sections, as well as the San Juan Metro
area.
By Wednesday, weather conditions become more typical, with PWAT
values between 1.70 and 1.9 inches and relative humidity in the
700500 mb layer climbing above 60%, allowing for variable weather
of warm mornings with heat indices rising up to 108 degrees and
active evenings with thunderstorms and gusty winds from 12 to 5 PM.
By Thursday, conditions will evolve again as an upper- level low
moves northwestward across the Caribbean, increasing instability
over the region. Despite slightly lower moisture, with PWAT values
still around the climatological median, the presence of
instability will be sufficient to support scattered convection,
particularly during the afternoon hours across the interior and
northwestern Puerto Rico. Meanwhile, the synoptic pattern at the
surface will favor a persistent east- southeasterly wind flow,
with breezy conditions as suggest by the 925 mb wind speeds in the
model guidance, largely driven by the interaction between a
tropical system moving over the central Atlantic. This will
sustain a warm trend in the morning with an increase in heat
indices followed by afternoon thunderstorm development as the week
progresses.
&&
.AVIATION...
(18z TAFs)
AL94 will produce SHRA/TSRA across the CWA, affecting mainly JPS,
JBQ, and JSJ after 25/18z. For JBQ, this activity should reduce
CIGs and VIS, likely to promote MVFR/IFR conds btwn 25/21-26/01z,
and may return by 26/04z. MVFR/IFR conds could also prevail at
JPS btwn 2600/2606z due TSRA. VFR conds should persist for the
rest of the TAF sites. E- SE winds btwn 10 kt and gusts up to 22
kt will continue through 2523z, becoming light/var aft 25/23z, and
increasing btwn 10-15 kt around 26/12-13z.
&&
.MARINE...
The trailing moisture from AL94 will bring additional showers and
thunderstorms across the islands. Moderate to locally fresh winds
will persisted the east-northeast across the Atlantic and from the
southeast across the Caribbean Sea and Mona Passage. Mariners
should exercise caution near thunderstorms. Improving marine
conditions are forecast from Friday morning into Saturday.
&&
.BEACH FORECAST...
Beachgoers: please exercise caution on the north- and east-facing
beaches in Puerto Rico and the US Virgin Islands due to a moderate
risk of rip currents until late Friday night. Thunderstorms may
produce lightning in the area. If you hear thunder, seek shelter
indoors or find a safe location.
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&
$$
MORNING CREW...CAM/MNG
EVENING CREW...ICP/YZR

NWS SJU Office Area Forecast Discussion