Bo Tras Talleres, Puerto Rico Weather Forecast Discussion

454
FXCA62 TJSJ 280859
AFDSJU
Area Forecast Discussion
National Weather Service San Juan PR
459 AM AST Sun Sep 28 2025
.KEY MESSAGES...
* Another warm day is forecast today, with heat indices reaching
   111 to 114. Therefore, an Extreme Heat Warning will be in
   effect from 10 AM to 5 PM for the coastal and urban areas of
   Puerto Rico, and a Heat Advisory will be in effect for Culebra,
   Vieques, and the U.S. Virgin Islands for the same period.
* Localized afternoon convection is expected each afternoon from
   today through Monday.
* An extended period of northeasterly swell from Hurricane Humberto
   will continue to result in hazardous marine and coastal
   conditions from today through late tonight.
&&
.SHORT TERM...Today through Tuesday...
Scattered showers and isolated thunderstorms were noted across the
Mona Passage into the Caribbean waters and over the offshore
Atlantic waters during the early morning hours. Some of this
activity moved over the coastal areas of southwestern PR and St.
Croix. However, rainfall amounts were not significant. Minimum
temperatures ranged from the mid-60s across the higher elevations of
PR to the mid and upper 70s across the lower elevations. In the U.S.
Virgin Islands, temperatures were from the mid-70s to the low 80s.
Winds were light with a south to southwesterly component.
Another hot day is expected due to the combination of calm to light
winds with a southerly component, and as the 925mb temperature
remains well above normal, near 24C. Therefore, maximum temperatures
will again reach the low 90s across most coastal areas, and higher
dewpoints under weak sea breezes, particularly along the northern
coast of PR, will enhance the heat threat before the onset of
afternoon showers. Heat indices could increase up to 112F in those
areas. Hi-res and global models suggest limited shower activity
today over the islands; however, satellite data indicate that the
shallow band of moisture that produced the overnight shower and
thunderstorm activity is merging with an external rainband from TC
Humberto. As this moisture is pulled over the islands during the
day, afternoon convection is expected mainly over the Cordillera.
Under a weak southwesterly steering flow, the showers are expected
to drift northeastward into nearby municipalities.
Minor concentrations of Saharan dust are expected to move over the
islands on Monday. Although the precipitable water content is
forecast to range from below normal to normal levels, the 850-700 mb
lapse rates are expected to remain in the 50th percentile throughout
the period. Therefore, a similar weather pattern is expected
throughout the short-term period. However, as winds pick up from 10
to 15 knots from the east to southeast, the focus of afternoon
convection will shift once again over west/northwest PR. In
addition, another band of moisture associated with distant Humberto
is still expected to increase shower activity across the USVI and
eastern PR between Monday night and Tuesday morning.
.LONG TERM...Wednesday through Sunday...
On Wednesday, at the surface, a high-pressure system will combine
with the extended influence of Hurricane Humberto, maintaining a
southeasterly wind flow across the region at least until early
Thursday. This surface pattern will favor a variable weather
regime with patches of fragmented moisture moving in and out of
the area. Precipitable water values on Wednesday are forecast to
range between 1.5 and 1.7, near the 25th percentile. From Thursday
into Friday, global model guidance continues to suggest an
interesting mix of patterns. At the surface, lapse rates between
850 and 700 mb indicate a stable pattern, with values dropping two
standard deviations below climatological normals. In contrast,
the mid-to-upper levels will exhibit increased lapse rates between
700 and 500 mb and colder 500 mb temperatures, ranging from -6 to
-7 degrees. Although this pattern supports afternoon convection,
 models continue to show limited moisture with precipitable (PWAT)
 of 1.50 inches. This pattern basically suggest a typical weather
 pattern with localized showers, particularly across northwestern
 Puerto Rico on Thursday.
On Friday into Sunday, veering surface winds are expected as the
tail of a tropical system moves eastward into the northeastern
Atlantic, weakening the surface high pressure diminish the
pressure gradient result in variable winds for the remainder of
the period. Therefore, on Friday, winds will become from the
north, inducing an advective pattern with sowers along northern
coastal areas in the morning and early evening hours. A rapidly
change will occur on Saturday, winds return from the east,
changing the weather pattern again. On Sunday, an increase in
tropical moisture with precipitable water values peaking up to 2
inches. So far today, Sunday looks like the wettest day of the
long term.
&&
.AVIATION...
(06Z TAFS)
Mainly VFR conditions are expected across all terminals during the
next 24 hours. However, iso TSRA/SHRA over central PR should cause
mostly VCTS across the PR terminals btw 28/17-21. Otherwise, VCSH
expected early in the fcst at TJPS/TISX/TIST. S-SW winds up to 13 kt
will continue mainly blo FL050.
&&
.MARINE...
Hazardous marine conditions continue due to a long-period
northeasterly swell generated by Major Hurricane Humberto, located
well to the north of the region. Seas will remain between 7 and 8
feet across the Atlantic waters and the Anegada Passage. A Small
Craft Advisory remains in effect through midnight. Improving
marine conditions are forecast from Monday into the workweek.
However, by midweek, model guidance suggests another northwesterly
swell will reach the local waters, deteriorating conditions once
again.
&&
.BEACH FORECAST...
Extremely hazardous coastal conditions are expected along the
northern and northeastern coasts, with breaking waves exceeding 10
feet. A High Surf Advisory is in effect until 6 PM AST for Culebra
and St. Croix. A High Risk of Rip Currents is also in effect.
Elsewhere, the rip current risk will remain moderate through
tomorrow. Improving coastal conditions are forecast from late
Monday into Tuesday. By midweek, another northwesterly swell is
expected to reach the region, worsening coastal conditions again.
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through late tonight for PRZ001-002-005-
     008-012.
High Surf Advisory until 6 PM AST this evening for PRZ001-002-
     005-008.
Extreme Heat Warning from 10 AM this morning to 5 PM AST this
     afternoon for PRZ001>005-007-008-010-011.
Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for PRZ012-013.
VI...High Rip Current Risk through late tonight for VIZ002.
Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for VIZ001-002.
AM...Small Craft Advisory until midnight AST tonight for AMZ711.
Small Craft Advisory until midnight AST tonight for AMZ712.
Small Craft Advisory until 6 PM AST this evening for AMZ716.
Small Craft Advisory from noon today to midnight AST tonight for
     AMZ741.
&&
$$
SHORT TERM & AVIATION...DS
LONG TERM & MARINE....LIS

NWS SJU Office Area Forecast Discussion