National Weather Service Today's Weather Impact Levels

536
FXCA62 TJSJ 240855
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
455 AM AST Mon Mar 24 2025

.SYNOPSIS...

High pressure at all levels will continue to dominate through
midweek. Patches of moisture embedded within the breezy trades
will still bring showers to windward areas during the first part
of the workweek. Wednesday will bring an uptick in shower activity
as larger patches of low-level moisture spread across the region.
An unstable weather pattern could prevail by the second part of
the week with the arrival of a mid to upper-level trough and a
frontal boundary. The breezy winds will promote choppy seas, small
craft should exercise caution. Small craft advisories will be in
effect tomorrow for the offshore waters and local passages.

&&

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

High pressure at all levels will continue to dominate through
midweek, as seen in GOES Water Vapor imagery showing a dry signature
over the eastern and central Caribbean. This setup will maintain
stable conditions aloft, while surface high pressure over the
northeast Atlantic supports breezy to windy trade winds, especially
along the tropical Atlantic and eastern Caribbean. Today is expected
to be the driest day, with below-normal moisture leading to mostly
sunny skies and limited shower activity.

By Tuesday, moisture embedded in the brisk trades will bring
scattered showers, mainly over windward areas and the US Virgin
Islands. A few patches of clouds and showers will move across the
northeast Caribbean, but mid-level stability will keep rainfall
light and brief. Showers will remain shallow, with limited vertical
development due to the ridge aloft.

Wednesday will bring an uptick in shower activity as larger patches
of low-level moisture spread across the region. Operational models
show an increase in trade wind showers, with an upper-level trough
moving in from the west, weakening the high pressure and increasing
instability. TJSJ sounding data shows fast steering winds around 20
knots, this will keep showers moving quickly and preventing
prolonged rainfall in one area, reducing the flooding risk.

.LONG TERM...Thursday through Monday...

Current model guidance suggest the approach of an area of relatively
drier air, but with small patches of moisture embedded, under up
to breezy east to east-southeast steering flow arriving to start
the period. However, a strong surface high will be in place over
the central Atlantic will gradually be displaced by another
surface high moving into the western Atlantic to start the period.
The general diurnal pattern (with overnight and morning trade
wind showers moving over windward sectors of the islands and
afternoon convective showers mainly over west-northwest Puerto
Rico, on Thursday, due to diurnal heating, sea breeze convergence
and local effects) will be present during the period but will be
boosted by an increase in moisture and instability over the region
late Thursday and Saturday. Instability will increase due to a
mid to upper trough moving near the region from the west, by late
Thursday available moisture will go from being confined below 800
mb to reaching up to 400 mb. Moisture will increase due to a
frontal boundary or its remnants moving over the region, PWAT
values will increase to 1.5 in to 1.8 in over the islands. The
steering flow is forecast to back and become more northeasterly by
Saturday and Sunday, causing afternoon convection to concentrate
over west to southwest PR. Model guidance suggest a drying trend
by Sunday and another uptick in moisture on Monday as the steering
flow gradually veers to become east-southeasterly. 925mb temperatures
will be at normal to above normal values to start the period.

&&

.AVIATION...

(06Z TAFs)

VFR conditions are forecast to prevail across all TAF sites. Brief
trade wind showers may affect USVI terminals and TJSJ through 15Z.
VCSH at TJBQ and TJMZ possible between 17Z-21Z. Mainly E winds
around 20 kt with occasional higher gusts will prevail below FL150.

&&

.MARINE...

A surface high pressure will build across the Central Atlantic,
tightening the local pressure gradient and promoting moderate to
fresh trade winds throughout most of the week. A northwesterly to
northerly swell will gradually dissipate today. However, the moderate
to fresh winds will promote choppy seas; small craft advisories will
be in effect tomorrow for the offshore waters and local passages.

&&

.BEACH FORECAST...

The northwesterly to northerly swell continues to dissipate,
however a moderate risk of rip currents remains for most of the
coastlines, today due to increased winds. Up to a moderate risk
of rip currents is forecast for the rest of the week, meaning
that life- threatening rip currents are possible in the surf zone.
For more information, please refer to the latest Coastal Hazard
Message (CFWSJU) and the latest Surf Zone Forecast (SRFSJU).

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...Small Craft Advisory from 6 AM Tuesday to 6 AM AST Wednesday for
     AMZ711-723-733-741.

&&

$$

SHORT TERM...ERF
LONG TERM....MRR

NWS SJU Office Area Forecast Discussion