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000
FXCA62 TJSJ 100142
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
942 PM AST Tue Apr 9 2024

.UPDATE...
Moisture remnants along the frontal boundary with few embedded
showers continued to sink southwards across the islands an into
the local waters of the Caribbean during the late evening hours.
Meanwhile the high pressure ridge continued to build and spread
across the west Atlantic increasing the northeast trade winds.
Periods of passing showers can be expected overnight with brief
wind gusts possible accompanying the shower activity which may
affect parts of the north and east coastal sections of Puerto Rico
as well as portions of the U.S. Virgin Islands. Periods of moderate
to locally heavy rains may be possible at times as least into the
early morning hours. On Wednesday a gradual drying trend is expected
with breezy conditions. Periods of passing showers and streamer-
like afternoon showers cannot be ruled out during the day,across
parts of the interior and southwest sections of Puerto Rico,as well
as on the west end and downwind of the U.S.Virgin Islands. Otherwise
no change to the inherited short term forecast and reasoning.

&&

.AVIATION UPDATE...VFR conds durg prd. SCT OCNL BKN lyrs nr
FL025...FL050 and BKN-OVC nr FL090 as the frontal boundary
continued to cross the local flying area. Few embedded SHRA psbl
en route btw islands, especially btw ERN PR and the USVI terminals.
SFC wnd fm E-NE 10-15 kts with ocnl hir gusts and accompanying
passing SHRA. VCSH psbl at TJSJ/TJBQ and USVI terminals durg prd.

&&

.PREV DISCUSSION... /issued 512 PM AST Tue Apr 9 2024/

SYNOPSIS...
A surface high building across the western Atlantic will promote
passing showers through tonight, however an improvement in weather
conditions are expected by midweek as drier air arrives. However,
the remnants of the cold front will return by the end of the
workweek, increasing the chances for rainfall activity again.
Starting tonight, moderate to locally strong winds and northerly
swell will deteriorate marine and beach conditions. High surf
conditions are expected tomorrow afternoon through at least
Thursday.

SHORT TERM...Tonight through Thursday...

A building surface high across the western Atlantic will continue
to support moderate to locally fresh northeasterly winds tonight,
pushing residual moisture across the region. This will cause
passing showers to continue through tomorrow mainly effecting
coastal windward sections of eastern Puerto Rico and the USVI.
Afternoon convection is forecast for tomorrow afternoon,
particularly across the interior to southwestern Puerto Rico,
although continued cloudiness during the morning hours can serve
to limit it. This activity however, can still result in ponding of
water on roads and poorly drained areas, as well as urban and
small stream flooding, especially with the heaviest activity.
Temperatures are forecast to be cooler under breezy NE winds.

A drying pattern is forecast on Thursday with PWAT values/overall
vertical moisture content decreasing. We expect Thursday to be
the driest day of the week with shower activity affecting windward
sectors with more limited convective activity over interior to SW
PR during the afternoon. By Thursday night and into
the long term period another patch of moisture, remnants of the
past frontal boundary, will filter into the region to bring back a
showery pattern. Expect windy conditions over these days as the
surface high pressure continues to strengthen north of the
region.

LONG TERM...Friday through Tuesday...
/from previous discussion/

Model guidance suggests precipitable water values at or above
normal levels, except between Saturday evening and Monday morning.
This wet pattern results from distancing the mid-level ridge early
in the period, followed by the proximity of an upper-level trough
and associated jet early next week. The general steering flow at
lower levels should remain from the east throughout the period,
generated by a broad surface high pressure spreading across the
North Atlantic. However, as this feature weakens, wind speeds are
projected to weaken from 15-25 mph to 5-15 mph early next week.

In the expected scenario, heightened passing shower activity is
likely on Friday and from Monday onwards, affecting northern and
eastern sections of the local islands, with less frequent to
limited passing shower activity during the weekend. Afternoon
convective development is likely each, even during the driest
periods, with the highest impact across the western interior to
western Puerto Rico. Given the uncertainty in the forecast
associated with the timing of the wettest periods and the effects
of the upper-level trough, the excessive rainfall risk was kept at
low levels. However, the risk could elevate with a more direct
influence, and flooding impacts could start as early as Tuesday.
Breezy conditions will prevail through the weekend, leading to
limited wind impacts, mainly across coastal areas. Temperature
variations, in turn, should remain within seasonal levels
throughout the period.

AVIATION...
(TAFs 18z)

Mostly VFR conditions expected through the forecast cycle.
SHRA/isold TSRA ovr ctrl mtn range, spreading to S and SW PR may
cause MVFR or even IFR conds at JPS. Passing SHRA may affect
JSJ/IST/ISX. ESE winds 15 to 20 knots with higher gusts, becoming at
10 to 15 knots overnight.

MARINE...

A surface ridge building across the western Atlantic will cause
fresh to locally strong northeast winds throughout the workweek,
causing an increase of passing showers and brief gusty winds. A
northerly swell will begin to arrive tonight, strengthening
through tomorrow meanwhile another long period northerly swell
begins to arrive on Thursday, together causing hazardous seas for
small craft for the rest of the week. For details, refer to the
Marine Weather Statement (MWWSJU).

BEACH FORECAST...

Increasing winds and the arrival of a northerly swell will
deteriorate beach conditions starting this evening, mainly across
the north-facing beaches. Tomorrow, conditions will worsen with
large breaking waves exceeding 10 feet by the afternoon hours,
causing hazardous swimming conditions, as well as localized
coastal flooding and beach/dune erosion. For details, refer to the
Coastal Hazard Message (CFWSJU) and Surf Zone Forecast (SRFSJU).

&&

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

     High Surf Advisory from noon Wednesday to 6 PM AST Thursday for
     PRZ001-002-005-008-010-012.

     High Rip Current Risk from Wednesday afternoon through late
     Thursday night for PRZ013.

VI...High Rip Current Risk through late Thursday night for VIZ001.

     High Surf Advisory from noon Wednesday to 6 PM AST Thursday for
     VIZ001.

     High Rip Current Risk from Wednesday afternoon through late
     Thursday night for VIZ002.

AM...Small Craft Advisory until 6 AM AST Friday for AMZ711-712-716-
     723-741-742.

     Small Craft Advisory from noon Wednesday to 6 AM AST Friday for
     AMZ726.

     Small Craft Advisory until 6 AM AST Friday for AMZ733.

&&

$$

SHORT TERM...RAM
LONG TERM....MMC
AVIATION...RAM