National Weather Service Today's Weather Impact Levels

240
FXCA62 TJSJ 220859
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
459 AM AST Wed Jan 22 2025

.SYNOPSIS...

Shower activity is expected to increase in general through early
Thursday morning due to a trade wind perturbation. Choppy wind-
driven to hazardous seas will persist for most of the workweek,
maintaining dangerous conditions for small craft and promoting
life-threatening rip currents. Quick passing showers are expected
to move from time to time over the USVI and eastern sections of
PR. Shallow afternoon convection is possible over western PR each
day.


&&

.SHORT TERM...Today through Friday...

Mostly fair weather, and breezy conditions, were observed overnight
with passing showers embedded in the trades along eastern portions
of Puerto Rico and the U.S. Virgin Islands. Doppler radar rainfall
estimates ranged from 0.1 to 0.2 inches, with local amounts up to
0.3 inches over Rio Grande. Minimum temperatures in lower elevations
remained in the 70s while higher terrains were observed in the lower
to mid 60s.

The short term forecast remains on track, with a variable weather
pattern for the second part of the workweek. Current satellite image
shows patches of moisture arriving into the region, and derived
products show high moisture content over east of the Leeward
Islands. The broad high surface pressure in the Central Atlantic
continues promoting trade winds, which will remain for the next few
days. A mid-to-high level ridge northeast of the region will
maintain stable conditions aloft, unfavoring convection activity.
The perturbation in the trades is expected to arrive later today,
increasing PWAT values will increase up to 1.8 inches, above normal
values based on the latest model guidance and climatology. This will
promote frequent shower activity, from moderate to locally heavy,
across the region, particularly starting today in the afternoon into
Thursday morning. Rainfall accumulations over the eastern,
eastern interior, and the San Juan Metropolitan Area in Puerto
Rico, Vieques, Culebra, and the U.S. Virgin Islands. Although
showers will move quickly, ponding of water in roadways, urban,
and poorly drained areas is very likely, along isolated urban and
small streams flooding. A drier air mass will arrive on Thursday,
but patches of moisture will arrive bringing occasional showers.

Low-level winds shifting from the E-ESE will promote above-normal
925 mb temperatures today, with maximum temperatures in lower
elevations from mid 80s to upper 90s, and higher terrains from mid
70s to low 80s.

.LONG TERM...Saturday through Wednesday...

A deep-layered ridge is expected to presist over the Tropical
Atlantic throughout the long-term period. A short-wave trough is
expected to cause a brief weakness aloft over the region on
Sunday, and a pre-frontal trough is expected to develop mainly
north of the region during the weekend. Another upper level trough
is expected to move over the area on Tuesday, and the 500 mb
temperatures are forecast to drop near -7C. However, the
precipitable water content is forecast to remain at normal to
below normal levels through the entire forecast period, and
showers across the area will be driven mostly by the remnants of
old frontal boundaries that the trade winds will carry from time
to time.

Normal to above-normal temperatures are expected to prevail
throughout most of the long-term period, particularly in the
coastal and lower elevations of the islands. Daytime highs will
range from the mid to upper 80s and low 90s in coastal and urban
areas, while the mountains will experience highs in the mid to
upper 70s. Minimum temperatures will range from the low 60s in the
higher elevations to the mid and upper 70s in the lower elevations
of the islands.


&&

.AVIATION...

(06z TAFs)

Mostly VFR conds expected at TAF Sites. Perturbation in the trades
will arrive today, with -RA/+RA for TISX, TIST starting at 22/13z
and for TJSJ at 22/22z. Reduced CIG/VIS may promote brief periods of
MVFR conds from 22/18z to 23/06z. E-ESE winds from 8-12 kt and
gusty winds up to 20 kt.


&&

.MARINE...

A surface high pressure across the central Atlantic will support
moderate to locally fresh easterlies for the next several days.
Choppy wind-driven to hazardous seas for small craft will continue
across portions of most local waters and passages. Small craft
advisory conditions are likely to continue through the end of the
workweek. Increased shower activity will continue through early
Thursday morning.


&&

.BEACH FORECAST...

A high risk of rip currents is in effect for the north oriented
beaches of Puerto Rico, as well as for Culebra and easternmost
Vieques. A moderate risk of rip currents is in effect for most
other areas. Choppy wind-driven seas will continue to promote up
to a high risk of rip currents through the end of the week.


&&

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

VI...High Rip Current Risk through late Thursday night for VIZ002.

AM...Small Craft Advisory until 6 AM AST Friday for AMZ711-723.

     Small Craft Advisory until 6 AM AST Thursday for AMZ712-716-726-
     733-741.

&&

$$

SHORT TERM...MMC
LONG TERM....DS
AVIATION...MNG

NWS SJU Office Area Forecast Discussion