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000
FXCA62 TJSJ 150728
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
328 AM AST Mon Apr 15 2024


.SYNOPSIS...
A wet, unstable pattern is forecast for today through at least
Wednesday as a broad surface trough crosses the eastern Caribbean.
Tuesday and Wednesday appear to be the worst days of weather.
Heavy showers and thunderstorm activity with quick river
rises and water surges with flash flooding, and landslides are
possible. Conditions should improve by Thursday into the weekend.
Marine conditions across the Atlantic Waters remain hazardous for
small craft.

&&

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

A surge of moisture along the leading edge of a broad surface trough
crossing the eastern Caribbean brought increasing cloudiness with
frequent showers and periods of moderate to locally heavy rains to
the islands overnight into the the early morning hours. So far
rainfall accumulations ranged between a quarter of and inch to half
an inch with the heaviest rains. This lead to ponding of water on
roads and in poor drainage areas. Early morning low temperatures
were in mid to upper 70s along the coastal areas and in the upper
60s to low 70s in higher elevations. Winds were generally from the
east northeast between 5 to 10 mph but occasionally higher with the
passing showers.

For the rest of today, expect the trough to continue to cross the
region, but expect a break in cloud cover and diminishing showers by
late morning. However this will be short lived,as the moist east
southeast wind flow will increase moisture convergence during the
afternoon hours and continue through Tuesday and Wednesday. In
addition the approach of an amplifying mid to upper level trough and
colder temperatures aloft will further increase instability through
the period. That said, gradually increasing cloud coverage and
shower development is forecast to begin once again across portions
the USVI, northeastern, interior, and west to southwest Puerto Rico
during the afternoon through the rest of the period.  Recent
Satellite imagery and derived layered precipitable water products
suggest increasing values to well above normal and in excess of 2.0
inches through Tuesday then gradually tapering off to between 1.60-
1.80 by Wednesday based on recent model guidance. This high and deep
layered moisture content along with the increasing instability and
cold air advection aloft will persist during the entire period,
resulting in high potential for flooding rains and quick rises along
rivers and streams along with mudslides and rockfall in areas of
steep terrain.

For Tuesday and into Wednesday, weather conditions are forecast to
continue to deteriorate and become even more unstable as the upper-
trough approaches from the northwest and interacts with the moisture
pooling and low level convergence. Model guidance continued to
suggest 500 mb temperatures ranging between -7.0 to -9.0 degree
Celsius during the period, thus promoting even higher potential for
isolated to scattered but strong to even near severe thunderstorm
activity possible with best potential for heavy rainfall activity
being later this afternoon and continuing through Tuesday.

By Wednesday, a slow but gradual erosion of moisture is so far
forecast. However despite the diminishing moisture convergence
across the region which should shift north and east of the area, the
still fairly moist and unstable weather conditions will combine with
diurnal heating and local effects, and increase convective
development during the late morning and afternoon hours. This will
lead to more localized showers and isolated thunderstorms with
periods of locally heavy rains to remain possible as well as the
potential for n additional urban and small stream flooding along
with mudslides and rockfall in areas of steep terrain, particularly
in urban and flood-prone areas.

To sum it all up...there is high confidence that this expected
unsettled weather pattern for the period will lead to quick river
rises and water surges with flash flooding, and landslides likely.
The wettest period so far is later today and through Tuesday or
early Wednesday. Residents especially those in flood prone areas are
encouraged to review and prepare their flood back up plans in and
around their homes and en route in case heavy rains do occur in
their area during the period.

&&

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

As the influential surface-induced perturbation and associated
mid to upper-level through begins to move well to the northeast of
the region, weather conditions will begin to improve on Thursday.
The arrival of drier air and a building mid to upper-level ridge
across the western Caribbean will reinforce a more stable weather
pattern Thursday onward. Meanwhile, a surface ridge builds across
the west Atlantic to continue the trend of east-northeast winds
once again through Friday, followed by winds becoming more
easterly and increasing over the weekend. Weather conditions will
consist of the occasional passing trade wind showers and more
typical isolated to scattered afternoon showers in and around the
islands over the weekend. On Monday a moist airmass may begin to
lift across the eastern Caribbean, bringing a wetter pattern
throughout the following week.

&&

.AVIATION...
(06z)

SHRA/Isold TSRA will increase across the region through fcst prd due
to a surface trough crossing the region today and later interacting
with an amplifying upper trough and cold frontal boundary
approaching from the northwest. Prds of reduced VIS to btw 3-5 SM
and LOW CIG will be psbl with SHRA/Isold TSRA, especially en route
to and at USVI terminals and TJSJ til 15/14Z. Isold TSRA expected
ovr Atl waters and local passages btw islands with MTN TOP OBSCR
durg morning and aftn convection.  Isold VCTS aft 15/17Z TJBQ/TJMZ.
Winds will be from E 5-10 kts hir w/ passing SHRA bcmg ESE at 12-18
kts, with stronger gusts aft 15/14Z.


&&

.MARINE...
A surface ridge over the north-central Atlantic and
broad surface trough across the eastern Caribbean will generate
moderate to locally fresh east-northeasterly winds. A fading
northerly swell and the choppy wind driven seas will continue to
promote confused seas across the Atlantic waters. An approaching
upper level trough and induced surface trough will continue to
promote inclement weather across the local waters for the next few
days.


&&

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

VI...None.
AM...Small Craft Advisory until 6 AM AST Wednesday for AMZ711.

     Small Craft Advisory until 6 PM AST this evening for AMZ723.

&&

$$

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