Vieques, Puerto Rico Weather Forecast Discussion

158
FXCA62 TJSJ 291858
AFDSJU
Area Forecast Discussion
National Weather Service San Juan PR
258 PM AST Mon Sep 29 2025
.KEY MESSAGES...
* Moisture trailing distant Humberto will continue to affect the
  region early this workweek, bringing showers and possible
  isolated t-storms from the Caribbean sea under Southeasterly
  winds.
* Afternoon showers with few isolated thunderstorms will also
  continue developing along the central and northern
  municipalities of Puerto Rico.
* For the U.S Virgin Islands, expect passing showers to continue,
  especially later tonight, across the islands.
* At least an elevated heat risk will continue each late morning
  to afternoon during the next few days.
* A large, long period northerly swell will promote hazardous seas
  and life-threatening rip currents from late Thursday through
  Sunday.
&&
.SHORT TERM...Tonight through Wednesday...
Calm weather conditions prevailed during the morning hours under
mostly sunny to partly cloudy skies. A few showers developed over
the Caribbean waters and moved over portions of southwestern Puerto
Rico. Doppler radar estimated rainfall accumulations of less than
0.50 inches over Guanica and Lajas. Later in the afternoon, isolated
to scattered showers continued to move from the Caribbean waters
into portions of southern and southeastern Puerto Rico and the U.S.
Virgin Islands. These showers were fast-moving, resulting in only
minor accumulations across the aforementioned areas. Maximum
temperatures reached the upper 80s to low 90s along the coastal and
urban areas, with heat indices surpassing 105 degrees Fahrenheit in
those regions. Winds were observed from the south-southeast (SSE) at
10 to 15 mph, with higher gusts at times.
For tonight, fair weather conditions will prevail across the area
with few passing showers moving from time to time over the local
waters and portions of eastern Puerto Rico and the U.S. Virgin
Islands. Minor concentrations of Saharan Dust will continue,
although decreasing overnight. By Tuesday onwards, similar
conditions will persist with calm weather during the morning
hours, followed by afternoon convective activity over portions of
northwestern Puerto Rico. Streamer activity could also form during
the afternoon, affecting the municipalities of the San Juan
metropolitan area and adjacent regions. A warm trend is
anticipated for the next several days under a south- southeasterly
wind flow, in response to Major Hurricane Humberto, which is
located well far north of our area. Under this pattern, the 925 mb
temperatures are expected to remain above-normal through the
week. A Heat Advisory or Extreme Heat Warning is likely during the
upcoming days across the islands. Therefore, people sensitive to
heat will be affected, especially those without effective cooling
or adequate hydration. Take extra precautions when outside.
.LONG TERM...Thursday through Monday...
/FROM PREV DISCUSSION...Issued at 518 AM AST Mon Sep 29 2025/
Some changes were introduced to the long-term forecast. The wind
pattern will likely vary due to weather features inducing a col area
that should move over the CWA and promote lighter winds through at
least Sunday. A drier air mass filtering into the region and the
influence of a mid to upper level ridge will drop relative humidity
values and suppress deep convection activity, promoting stability
aloft. Based on the deterministic guidance of the GFS and ECMWF,
Precipitable Water (PWAT) values should stay between below-average
and seasonal values (1.5 - 1.7 inches, lower chance reaching 1.8
inches), but daytime heating combined with local effects could
lead to shower activity each day by midday into the afternoons.
Although deep convection activity may be limited, 500 mb
temperatures may cool and remain seasonal (-6 and -7 degrees
Celsius), increasing chances of isolated thunderstorms during the
afternoons. Due to winds becoming lighter, any shower activity
will likely remain stationary, increasing the flooding potential.
Hence, the flooding threat will remain limited to elevated over
the aforementioned areas. Moisture content will gradually increase
by Monday due to the approach of a vigorous tropical wave to the
CWA. Although theres variability between ensemble members,
theres a tendency for PWAT values to increase up to near above-
normal values (1.8 - 2.0 inches).
With well-above-normal 925 mb temperatures, slow SE-S winds, and
available moisture, heat indices are very likely to exceed 100
degrees Fahrenheit and reach Heat Advisory Criteria. Therefore, the
heat threat will remain elevated for the rest of the forecast
period.
&&
.AVIATION...
(18Z TAFS)
Mainly VFR conds expected across all terminals during the next 24
hrs. Afternoon SHRA/TSRA are possible in the VCTY of TJBQ/TJPS thru
29/30Z. Brief MVFR conds are possible with the strongest activity.
VCSH to continue for TIST/TISX thru 29/22Z. HZ due to Saharan dust
will be present across the area, however, visibilities will remain
at P6SM. SSE wind btw 10-12 kts with higher gusts thru 29/22-23Z.
Winds will be light and variable overnight thru 30/14Z.
&&
.MARINE...
The long-period northerly swell from distant Major Hurricane
Humberto continues to subside. Moderate southeasterly to easterly
winds will continue for the next few days, becoming gentle by the
end of the workweek. A large northwesterly swell will promote
hazardous marine conditions by late Thursday night through the
weekend.
&&
.BEACH FORECAST...
The long-period northeasterly swell from distant Major Hurricane
Humberto continues to subside. There is a moderate risk of rip
currents across the northern beaches of Puerto Rico, as well as
Culebra, St. Thomas and St. John. Under a moderate risk, life-
threatening rip currents are possible in the surf zone. Conditions
will gradually improve tonight as most beaches are forecast to be
under a low risk of rip currents tomorrow. Even if the risk for
rip currents is low, life- threatening rip currents often occur in
the vicinity of groins, jetties, reefs, and piers.
A large northerly swell will promote hazardous beach conditions
by late Thursday night through the upcoming weekend.
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>005-007-
     008-010>013.
VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.
AM...None.
&&
$$
MRR/GRS

NWS sju Office Area Forecast Discussion