Urb Jose H Ramirez, Puerto Rico Weather Forecast Discussion

819
FXCA62 TJSJ 291022
AFDSJU
Area Forecast Discussion
National Weather Service San Juan PR
518 AM AST Mon Sep 29 2025
.KEY MESSAGES...
* Another warm day is expected across the local islands, with heat
  indices exceeding 108 degrees Fahrenheit. Hence, a Heat Advisory
  is in effect for the urban and coastal areas of Puerto Rico and
  the U.S. Virgin Islands from 10 AM AST through 5 PM AST.
* For the U.S Virgin Islands, expect passing showers later tonight
  across the islands.
* A large, long period northerly swell will promote hazardous
  seas and life-threatening rip currents from late Thursday
  through Sunday.
&&
.SHORT TERM...Today through Wednesday...
Isolated to scattered showers and brief isolated thunderstorms were
noted overnight across the Caribbean waters. Showers moved briefly
over the southern sections of the islands. Minimum temperatures
ranged from the upper-60s across the higher elevations to the upper
70s and low 80s across coastal areas. The wind was light from the
south to southeast.
Minor concentrations of Saharan dust will move over the islands
today. However, the precipitable water content will remain at normal
to above normal levels as Hurricane Humberto, well north of the
area, continues to pull tropical moisture in a deep southerly wind
flow over the eastern Caribbean. Shower activity is expected to peak
from late this afternoon through tonight across portions of the USVI
and east/southeast PR, with locally induced afternoon convection
expected over northwest PR. Trade winds will return by Tuesday, but
will turn once again from the south and become gentle to light on
Wednesday. Therefore, an elevated heat threat will persist across
the lower elevations of the islands. Maximum temperatures are
expected to reach the low to mid-90s each day across most coastal
counties. In terms of precipitation, a drier air mass is expected to
gradually fill from Tuesday into Wednesday, however, peaks on
moisture content are anticipated during the nighttime, favoring
showers across the windward areas of the islands. Also, locally
induced afternoon showers with isolated thunderstorms cannot be
ruled out over the NW quadrant of PR, particularly on Tuesday.
&&
.LONG TERM...Thursday through Monday...
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...
(06Z TAFS)
Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, tempo MVFR conds are possible at
TJBQ btw 29/18-22 due to -TSRA/SHRA over NW PR. Elsewhere, brief
periods of -RA/VCSH expected at times. HZ due to Saharan dust will
increase over the local area, but VSBY will remain P6SM. SSE winds
up to 12 kt with sea breeze variations expected after 29/13z.
&&
.MARINE...
The long-period northerly swell from Major Hurricane Humberto
continues to diminish across the region. 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 upcoming weekend.
&&
.BEACH FORECAST...
The long-period northeasterly swell from Major Hurricane Humberto
continues to diminish across the region. Although the rip current
risk downgraded to moderate across the northern beaches of Puerto
Rico, including Culebra, and St. Thomas and St. John in the U.S.
Virgin Islands, beachgoers are urge to exercise caution. A large
northerly swell will promote hazardous beach conditions by late
Thursday night through the upcoming weekend.
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for PRZ001>005-007-008-010>013.
VI...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for VIZ001-002.
AM...None.
&&
$$
SHORT TERM/AVIATION...DS
LONG TERM...MNG
MARINE/BEACH FORECAST...DS/MNG

NWS SJU Office Area Forecast Discussion