Villa Palmira, Puerto Rico Weather Forecast Discussion

048
FXCA62 TJSJ 211850
AFDSJU
Area Forecast Discussion
National Weather Service San Juan PR
250 PM AST Sun Sep 21 2025
.KEY MESSAGES...
* Heat Advisory to Extreme Heat Warning conditions are expected
  once again on Monday across the coastal counties of PR and the
  USVI.
* Across the USVI, fair weather conditions are expected to prevail
  in general with brief passing showers at times.
* Hazy skies are expected on Monday due to minor to moderate
  concentrations of Saharan dust.
* A tropical wave with a low chance of formation into a tropical
  system will bring an increase in shower and thunderstorm
  activity by midweek.
&&
.SHORT TERM...Rest of today through Tuesday...
Mostly sunny to partly cloudy skies prevailed across Puerto Rico
and the U.S. Virgin Islands this morning. Isolated thunderstorms
developed early in the afternoon hours, downwind from St. Croix
and from central to western Puerto Rico. Additional thunderstorms
are expected to continue across these areas through the rest of
the afternoon hours. Maximum temperatures were from the upper 80s
to mid-90s across the lower elevations of the islands, with heat
indices ranging between 108F-115F. Winds were light in general
with a southeasterly component.
For tonight into Monday, a drier air mass with suspended Saharan
dust embedded in a wind surge from the east will promote mostly
fair weather conditions across the islands. However, hazy skies
are expected through Monday, and locally induced afternoon
thunderstorms are expected to develop once again over central and
western PR. These thunderstorms can produce strong gusty winds and
frequent cloud to ground lightning. Also, localized heavy rainfall
will lead to quick urban and small stream flooding. On Tuesday, a
strong tropical wave, located near 50W, will bring an increase in
shower and thunderstorm activity across the region. This tropical
wave currently has a low chance of development into a tropical
system, however, squally weather and periods of heavy rainfall
will increase with the wave passage from late Tuesday into
Wednesday. Earlier in the afternoon, convective development is
expected mainly over central and west/southwest PR as winds
acquire a northeasterly component ahead of the wave passage.
.LONG TERM...Wednesday through Sunday...
...From previous discussion issued at 525 AM AST Sun Sep 21
2025...
From Wednesday through Thursday, a tropical wave currently being
tracked by the National Hurricane Center will move across the
region, bringing an increase in showers and thunderstorm activity
across Puerto Rico and the U.S. Virgin Islands. As of now, the
system is located over the eastern Atlantic with a low probability
of development, with near 0% within 48 hours and around 30% over
the next 7 days. Additionally, a weak upper-level trough, combined
with southeasterly flow around the Atlantic ridge, will sustain a
steady influx of tropical moisture through early Friday. This
pattern supports a prolonged period of unsettled weather with
daily rounds of heavy rainfall and thunderstorms. Model guidance
suggests precipitable water values between 2.0 and 2.3 inches
(well above climatological normals), along with mid-level
temperatures of -7 to 8 degrees Celsius, enhancing the risk for
deep convection and potentially having limited to elevated risk of
flooding through Friday.
Given the prevailing wet pattern on previous days and the already
saturated soils, the main threats include flash flooding, rapid
river rises, and landslides in vulnerable terrain. While tropical
development appears more likely after the system passes east of
the region, the situation will be monitored closely with updates
from official sources such as the National Hurricane Center.
Temperatures are expected to gradually increase beginning Thursday.
Given the available moisture and prevailing conditions, a Heat
Advisory may be issued for Thursday, followed by a potential
Extreme Heat Warning on Friday. However, this will largely depend
on how the tropical wave evolves.
By Friday into Saturday, a gradual improvement in weather conditions
is expected as a drier air mass filters into the region, bringing
a temporary break in the unsettled pattern.
On Sunday, however, model guidance indicates that another tropical
wave may approach the region. While it is too early to determine
development potential, this system will need to be monitored
closely as it draws nearer.
&&
.AVIATION...
(18Z TAFS)
SHRA/TSRA in and around TJBQ may cause tempo MVFR to brief IFR
conditions thru 21/21z. Elsewhere, mostly VCTS expected thru early
this evening. Otherwise, mainly VFR conditions expected to prevail
through most of the period. HZ due to Saharan dust will increase
on Monday, but VSBY should remain P6SM. Light sea/land breeze
variations will prevail til 22/13z when east winds return between
10 and 15 kts.
&&
.MARINE...
Light winds with a southeast component will prevail today.
Increasing trades are expected to return early in the week. A
strong tropical wave will bring squally weather across the
regional waters from late Tuesday through late Wednesday night.
Increasing winds and choppy seas are expected with the wave
passage. Seas should remain at 4 feet or less in general through
the week. However, a fading northeasterly swell will keep seas up
to 5 feet tonight across the Atlantic waters.
&&
.BEACH FORECAST...
A fading northeasterly swell will maintain a moderate risk of rip
currents on Monday along the north facing beaches of Puerto Rico,
and return once again by midweek and spread across the rest of
the north and east facing beaches of PR and the USVI.
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Extreme Heat Warning until 4 PM AST this afternoon for
     PRZ001>005-007-008-010-011.
Heat Advisory until 4 PM AST this afternoon for PRZ012-013.
VI...Heat Advisory until 4 PM AST this afternoon for VIZ001-002.
AM...None.
&&
$$
SHORT TERM...DSR
LONG TERM....MMC
AVIATION...DSR
BEACH/MARINE...DSR

NWS SJU Office Area Forecast Discussion