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000
FXCA62 TJSJ 170841
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
441 AM AST Wed Apr 17 2024

.SYNOPSIS...

Unstable weather conditions are expected to prevail across the
local area through at least today. Showers and isolated
thunderstorms are also expected during the overnight hours.
Therefore, there is the potential for minor flooding, river rises
and mudslides due to soil saturation. Conditions should improve
tomorrow into the weekend, however wet conditions are expected
next week. Marine conditions will slowly improving across the
local waters, however, a northeasterly swell is forecast to
arrive Thursday.

&&

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

A broad surface trough extending across the northeast Caribbean and
surface high pressure over the southwest Atlantic will maintain
light east northeast winds across the area today into Thursday, then
forecast to become more easterly by Friday. A mid to upper level
trough will continue to slowly shift eastward across the region
through Thursday, then linger across the northern Leeward Islands by
Friday with another short wave trough forecast to cross the west
Atlantic and just north of the region by then. The proximity of the
upper trough along with the surface trough and a weak area of low
pressure now forecast to develop northeast of the region over the
next few days will support a fairly moist and unstable environment
through the period.

Recent satellite imagery and doppler weather radar showed mid to
high level cloudiness and light to moderate showers accompanying the
upper trough just west and north of the region, while fewer showers
were noted over the islands and coastal waters steered by the east
northeast winds. Shower activity continued to wane over land areas
overnight, while rivers and streams slowly subsided. However another
round of developing showers is expected to affect the islands later
this morning and during the afternoon aided by local and diurnal
effects. Early morning low temperatures remained in the mid to upper
70s along the coastal areas and in the upper 60s to low 70s in
higher elevations. Winds were calm to light and variable.

Through the rest of the period, unstable weather conditions are
forecast to continue, due to the meandering upper trough and good
low level moisture convergence. Present model guidance as well as
recent satellite derived precipitable water products and analyses
all suggest precipitable water values ranging between 1.70-1.85
across the region today. However this is forecast to gradually
diminish to between 1.65-1.70 inches by Friday favoring less
widespread shower activity and deep convection. The overall scenario
still suggests sufficient instability aloft and plenty of moisture
available for enhanced of overnight showers and isolated
thunderstorms across portions of the islands and local waters during
most of the period. Developing showers with periods of locally heavy
rains will be possible each day and any additional rains may lead to
ponding of water and flooding in flood prone areas as well as
quickly reacting rivers and streams along with water surges with
flash flooding, and landslides.

&&

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

Areas of low pressure spread across the central Atlantic basin and
developing surface high in the western Atlantic will maintain
moderate NE winds through the weekend along with enough water
content in a lingering airmass to allow passing showers and
afternoon convection to fire up due to diurnal heating and local
effects. By Sunday, an area of lower pressure near Florida will
assist the lifting of a moist airmass from the eastern Caribbean,
raising precipitable water values well above average values. This
in combination with a mid to upper-level trough, with the jet max
over the region through late Sunday, will allow an increase of
passing showers and afternoon convection mainly across western
Puerto Rico.

Winds begin to strengthen and veer, becoming more easterly to
southeasterly Monday to Tuesday, respectively, as the aforementioned
surface high moves into the central Atlantic. Due to all of this a
wet pattern is expected from Sunday onward with Wednesday containing
a best chance for widespread rainfall.


&&

.AVIATION...
(06z)

Wdly SCT SHRA/Isold TSRA psbl across the local flying area due to
proximity of a surface trough an upper trough slowly crossing the
region from the northwest. SCT-BKN lyrs nr FL025...FL050...FL080.
Brief MVFR conds psbl due to SHRA/LOW CIG nr SHRA en route to TJSJ
and USVI terminals during the early morning hours. Isold TSRA ovr
offshore Atl waters N of the islands. Brief MTN TOP OBSCR psbl ovr
Ern PR due to -RA/LOW cld lyrs til 17/14Z and over west and ctrl
interior of PR fm 17/16z-23Z. VCSH psbl at TJBQ/TJSJ and USVI
terminals durg prd. SFC Winds lgt/vrb bcmg fm E-NE 10-15 kts and
ocnly hir gusts aft 17/14Z.


&&

.MARINE...
A surface ridge over the north-central Atlantic and broad surface
trough across the eastern Caribbean will generate moderate to locally
fresh east to northeasterly winds through tonight. An upper level
trough and induced surface trough will continue to promote inclement
weather across the local waters over the next few days, with squally
weather and thunderstorms possible at times. A northeasterly swell
is forecast to arrive by tomorrow.


&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM...RAM
LONG TERM....RC