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000
FXCA62 TJSJ 120841
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
441 AM AST Fri Apr 12 2024

.SYNOPSIS...

Breezy conditions and passing showers will continue through
Saturday as the remnants of a front continues to cross the region.
Locally induced afternoon showers are expected during the weekend
over western PR, and from streamers developing off the
USVI/Eastern PR. A mid- to-upper-level trough and higher moisture
content are expected to increase shower and thunderstorm activity
across the islands from Monday through Wednesday. Hazardous seas
and life-threatening rip currents will continue for the next few
days.


&&

.SHORT TERM...Today through Sunday...

An overnight radar and satellite imagery analysis indicated
persistent shower activity affecting the area, with less frequent to
no showers across southwestern Puerto Rico. In the last 6 hours,
radar estimates indicated the highest rainfall totals, ranging
between 0.5 and 1.5 inches along an area stretching from central Toa
Baja westward to northern Barceloneta and around El Yunque National
Forest. As reported by official sites, overnight minimum
temperatures ranged from 65 degrees in higher elevations to 78
degrees across lower elevations. Winds were generally from the east
to east-northeast at 10-20 mph with gusts up to 25-30 mph across
windward areas, but light to calm and variable elsewhere.

The forecast for the short-term forecast period remains unchanged.
Breezy to windy east-to-east-northeast trade winds, driven by a
strengthening high-pressure system over the western-central
Atlantic, will continue to affect the area throughout the forecast
period, with wind speeds ranging from 15 to 25 mph at daytime,
diminishing to 10-20 mph at nighttime. Although a slight weakening
of this flow is likely during the weekend, breezy conditions will
persist. The prevailing wind flow will maintain an inflow of
moisture today, bringing precipitable water to above-seasonal levels
to approximately 1.8 inches this afternoon. A drier-than-normal
airmass will likely bring precipitable water values below seasonal
thresholds of around 1.0-1.2 inches by Sunday morning. However, this
will be short-lived, and an even wetter airmass will cause a spike
in moisture levels starting Sunday evening, with precipitable values
exceeding well above seasonal levels. The leading mid-level ridge
will gradually shift west-southwestward and away from the local
islands, steered by a mid-to-upper level trough sinking southward
across the western Atlantic. This transition should weaken the trade
wind inversion and allow moisture to ascend beyond the 700 mbar
layer. However, another ridge is forecast to cross the local islands
on Saturday, briefly supporting the reinstatement of the trade wind
cap.

Passing shower activity, driven by the prevailing flow, will
continue to affect most of the forecast area today. As the day
progresses, the focus of the showers will shift to central to
western Puerto Rico, as well as regions downwind from isolated
mountainous areas and the local islands. With conditions becoming
more favorable for deep convective development, afternoon showers
will likely produce significant rainfall totals of as much as 1.0-
2.0 inches across western Puerto Rico, where urban and small stream
flooding is likely. By tonight, the showers` focus will shift again
to the local waters and windward areas, producing isolated rainfall
amounts of up to half an inch. Temperatures should range from around
85 degrees at daytime to around 65 degrees at nighttime. Breezy to
windy conditions, as previously stated, will persist, with a limited
to elevated wind hazard risk across coastal areas and the local
islands, where unsecured or outdoor items could blow around or be
damaged.

Saturday is expected to follow a less showery weather pattern as a
drier-than-normal airmass begins to invade the region, followed by
an even drier and more stable weather pattern on Sunday morning.
However, as moisture levels rise and conditions become more
conducive for deep convective development by Sunday afternoon,
expect an increase in shower activity and, thus, higher rainfall
totals that could heighten flooding risks. Breezy conditions will
persist, posing a limited wind hazard risk.


.LONG TERM...Monday through Friday...

On Monday, the surface ridge over the central Atlantic will
weaken, and wind speeds will decrease as a front approaches from
the northwest. However, it will remain well north of the region.
At the same time, a mid-to-upper-level trough will move from the
southwestern Atlantic into the northeastern Caribbean and linger
over the area through midweek, providing good divergence aloft and
favorable dynamics for thunderstorm development as the 500 mb
temperatures are forecast to drop to around minus 8 degrees
Celsius. Meanwhile, an induced surface trough will develop over
the eastern Caribbean, leading to moisture pooling over the
islands. As a result, there is potential for thunderstorm activity
and flooding rains as a wetter and unstable pattern evolves
through at least late Wednesday night. According to model
guidance, there will be a quick drying trend from Thursday onwards
as an upper-level ridge builds from the western Caribbean,
promoting drier air intrusion and warming of the 500 mb
temperatures.


&&

.AVIATION...

(06Z TAFS) VFR conditions are likely across all terminals as trade
wind and afternoon SHRA affect the area. Expect these conditions
across TJSJ and USVI terminals throughout the period, after 12/16Z
at TJBQ, and after 12/23Z at TJPS. Prevailing E-NE winds at 10-20
knots increasing to 15-25 knots between 12/13-23Z, accompanied by
higher gusts and sea breeze variations. Higher winds and gusts are
likely near SHRA.


&&

.MARINE...

Fresh to locally strong east-northeasterly winds will continue
through early Saturday morning. Embedded in this wind flow, the
remnants of a front will bringing periods of passing showers and
brief gusty winds across the local waters. A fading northerly
swell and choppy wind-driven seas will continue to promote
hazardous conditions to small craft. Please refer to the latest Marine
Weather Message (MWWSJU) for detailed information. Seas are
forecast to improve briefly late in the weekend into early next
week.


&&

.BEACH FORECAST...

Dangerous swimming and life-threatening rip currents will continue
through at least Saturday across the east and north-facing
beaches of PR and the USVI, due to rough surf conditions with
breaking waves around 6 feet and higher at times. Given these
conditions, a High Rip Current Risk remains in effect for the
northwest to northeast beaches of the islands. Please refer to the
latest Coastal Hazard Message (CFWSJU) and Surf Zone Forecast
(SRFSJU) for detailed information. Beach goers should remain alert
as a moderate risk of rip currents will continue on Sunday across
across most east and northern beaches of the islands.


&&

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

VI...High Rip Current Risk through Saturday afternoon for VIZ002.

     High Rip Current Risk through this afternoon for VIZ001.

AM...Small Craft Advisory until noon AST Saturday for AMZ711-712-723-
     733-741.

     Small Craft Advisory until 6 AM AST Saturday for AMZ716-726-742.

&&

$$

AVIATION/SHORT TERM...ICP
BEACH/MARINE/LONG TERM....DSR