National Weather Service Today's Weather Impact Levels

213
FXCA62 TJSJ 130854
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
454 AM AST Mon Jan 13 2025

.SYNOPSIS...

While current long-period northerly swells are subsiding,
additional pulses are expected by tomorrow and will once again
deteriorate marine and coastal conditions throughout the second
half of the week. On the other hand overall generally fair weather
an cooler than normal temperatures are forecast for today. Tomorrow,
the remnants of an old frontal boundary to bring light to
moderate rains steered by northeasterly winds to the U.S. Virgin
Islands, Vieques, Culebra, and northern/eastern Puerto Rico in the
morning and early afternoon, tapering off by evening. Remnants of
past frontal boundaries are also forecast to move into the local
islands late Friday and into Saturday.

&&

.SHORT TERM...Today through Wednesday...

Radar and satellite imagery indicated mostly clear skies overnight,
with a few patches of low-level clouds moving across the region and
fog developing in the higher elevations of the interior after
midnight, likely affecting parts of highway PR-52 between Salinas
and Cayey. Although the broader wind flow remained from the
northeast, winds over land were light to calm and variable, with
land breezes dominating in coastal areas. Surface observations
showed overnight temperatures ranging from the mid-50s in the higher
elevations of the Cordillera Central to the lower 70s in coastal
areas and local islands.

A mid-level ridge drifting over the northern Caribbean will maintain
stable conditions throughout the period. Fair weather conditions are
expected today, with light to moderate northeast winds and minimal
to no shower activity. PWAT values will remain below normal, under
an inch. By Tuesday, the ridge`s influence briefly weakens,
coinciding with the remnants of an old frontal boundary to bring
light to moderate rains from trade wind showers to the U.S. Virgin
Islands, Vieques, Culebra, and northern/eastern Puerto Rico in the
morning and early afternoon, tapering off by evening. Rainfall
totals will be around a quarter inch, with improving conditions
after sunset. Northeast to north-northeast winds will strengthen
late Tuesday, becoming breezy.

The ridge will stretch back into the northeastern Caribbean by
Wednesday, while another surface high will yield increased trade
winds and wetter conditions. Trade wind showers will affect windward
areas, particularly at nighttime, with rainfall totals ranging from
a quarter to half an inch. Breezy to windy conditions will persist
throughout the day. Overall, temperatures will generally remain
cooler-than-normal, with overnight lows in the 50s in higher
elevations and 70s along the coast and daytime highs in the mid-80s.
For more details, visit the Experimental Graphical Hazard Weather
Outlook at https://www.weather.gov/erh/ghwo?wfo=sju.

.LONG TERM...Thursday through Sunday...

A surface high moving towards the western Atlantic will help
promote northeasterly steering flow to start the long term period.
Gradually increasing precipitable water (PWAT) values is
forecast, however they will still remain at below normal to low
end normal values before Friday, around 1.2 in to 1.3 in, with
only slightly more humid patches possible. Persistent mid-level
ridging and a trade wind inversion will continue to keep most
available moisture below 800 mb through most of the period.
Northeasterly winds will also promote a cooler temperatures across
the islands, with model- estimated 925 mb temperatures at below
normal to normal values. Maximum temperatures can reach the low to
mid 80s (locally higher) across lower elevation areas of the
islands. Minimum temperatures can reach the mid 50s to mid 60s
across higher elevations of Puerto Rico, and from the upper 60s to
mid 70s across lower elevations of the islands. Patchy fog can
also be present during the overnight to early morning hours across
sectors of interior Puerto Rico. With steering flow gaining a
more easterly component, remnants of past frontal boundaries are
forecast to move into the local islands from the east late Friday
and into Saturday, promoting above normal, 1.5 to 1.9 in,
precipitable water values and increased shower activity. Moisture
in this value will persist into the end of the long term period.
Limited flooding impacts continue to be possible during these days
as available moisture increases and shower activity is steered
into the area.

&&

.AVIATION...

(06Z TAFS)

VFR conditions with mostly clear to partly cloudy skies
will prevail. Increased cloud cover will focus along the Cordillera
Central and southern PR after 13/16Z, with minimal to no operational
impacts. Winds will be light to calm and variable overnight,
shifting from the NE and increasing to 10-12 knots with sea breeze
variations after 13/14Z, weakening after 12/23Z.

&&

.MARINE...

A surface high-pressure moving eastward across the western Atlantic
will promote light to moderate northeast winds over the next few
days. While current long-period northerly swells are subsiding,
additional pulses are expected by Tuesday and will once again
deteriorate marine conditions up to Small Craft Advisory criteria as
they spread across the Atlantic waters and local passages during the
second half of the workweek.

&&

.BEACH FORECAST...

While current long-period northerly swells are subsiding,
additional pulses are expected tomorrow, maintaining deteriorated
coastal condtions. A High Risk of Rip Currents will be in effect
today throughout the workweek for the beaches of northern Puerto
Rico, from Rincon to Fajardo, Culebra, St. Thomas and St. John. A
High Risk of Rip Currents is also forecast for St. Croix by
tomorrow night and last throughout the workweek. A High Surf
Advisory will possibly be issued for some exposed areas as we
approach the middle of the workweek.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Thursday afternoon for PRZ001-002-
     005-008-010-012.

VI...High Rip Current Risk through Thursday afternoon for VIZ001.

AM...Small Craft Advisory from noon Tuesday to 6 PM AST Thursday for
     AMZ711.

&&

$$

SHORT TERM...ICP
LONG TERM....MRR

NWS SJU Office Area Forecast Discussion