589
FXCA62 TJSJ 282155
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
555 PM AST Sun Apr 28 2024


.SYNOPSIS...

A surface high pressure over the western Atlantic will promote
breezy northeasterly winds through at least Wednesday. Drier
airmass between a surface low over the north central Atlantic and
the surface high should reach the local area under the northeasterly
fetch, but moisture content will oscillate between normal to
above-normal values. As a consequence, light to moderate showers
with isolated thunderstorms cannot be ruled out of the forecast.
By mid-week onwards, instability and moisture levels increase once
again as an upper level trough lingers over the western Atlantic
and lighter east to southeast winds return. Life-threatening rip
currents are expected during the first part of the week.

&&

.SHORT TERM...Tonight through Tuesday...

Today, partly cloudy skies were observed across the islands. Isolated
showers developed in the morning hours in areas from the central
north to the interior of Puerto Rico, the local islands, and
surrounding waters. Then, a line of showers developed northeast of
Vieques moving toward the southeast coast of Puerto Rico. Moving
to the afternoon hours, rainfall development was seen through
portions of the interior and southwest Puerto Rico due to lingering
moisture, daytime heating, and local effects. Based on the TJUA
radar rainfall estimates, accumulations today were around 1 to
1.50 inches across southwestern municipalities such as San Germn,
Sabana Grande, Guayanilla, and Peuelas. Values between 0.01 to
0.25 inches were recorded in the rest of the forecast area, while
northwest PR remained mostly dry.

For tonight, expect additional showers to move across north-
central and eastern Puerto Rico. Winds will continue from the
northeast between 10 to 15 mph with gusts of approximately 25 mph
or higher through mid-week. Then, shifting from the east on
Wednesday and becoming lighter.

Variable weather conditions are anticipated for the short-term
period, as a broad surface high pressure moves offshore the
eastern coast of the U.S. towards the Central Atlantic. This
weather feature will promote a slightly drier airmass to spread
into the region. Nonetheless, models are now showing that
precipitable water content values will not drop significantly, but
instead will oscillate between seasonal to above-normal values. As
a consequence, light to moderate showers with isolated
thunderstorms cannot be ruled out of the forecast every afternoon
across portions of the interior and southwest Puerto Rico.

&&

.LONG TERM...Wednesday through Sunday...
.FROM PREV DISCUSSION.../issued 455 AM AST Sun Apr 28 2024/

A more unstable and wetter pattern is expected to evolve during
the long term period as a mid-to upper-level trough develops and
remains nearly stationary over the west/southwestern Atlantic. By
Wednesday, the surface high pressure north of the area is
expected to weaken and in response winds are expected to veer from
the southeast, and become lighter through the rest of the period.
Meanwhile, old frontal boundaries and a restrengthening of the
surface low over the north central Atlantic will induce weak
troughs or perturbations across the northeastern Caribbean through
the end of the workweek. Steering winds will acquire a westerly
component and convective development with heavy showers are
possible over portions of the eastern interior, San Juan and
vicinity and over the USVI, particularly on Thursday and Friday.

Having said that and based on the latest guidance, all afternoons
through the long term period should be active with possible
flooding impacts and mudslides in areas of steep terrain across
Puerto Rico. For the USVI, an increase in the frequency of
showers and isolated thunderstorms is possible from Thursday
onwards. Heat indices across the lower elevations of the islands
could likely range between 102-106 degrees on Friday and Saturday
before the onset of afternoon convection.

&&

AVIATION...
(18Z TAFs)

Expect -SHRA to continue for the next hour or so across TJSJ and
TJPS followed by VCSH possible. Winds around 6 to 10 knots
overnight, but breezy conds are expected to return tomorrow
morning with winds out of the NE at 13-17 kts, and stronger gusts
throughout the day along with VCSH.

&&

MARINE...

Northeasterly moderate to fresh winds should prevail through at
least late Tuesday as a surface high pressure moves off the U.S.
East Coast. Then, becoming easterly and slightly diminishing by
Wednesday. These increasing winds and a northerly swell spreading
across the local waters on Monday will further deteriorate seas
through at least mid-week. Small Craft Advisories are in effect
for the Atlantic waters, the Mona Passage, waters north of
Culebra and St. Thomas, and the Anegada Passage.

&&

BEACH FORECAST...

Short-period waves and onshore flow along the northern and
eastern beaches of the islands will promote a moderate risk of rip
currents to continue this afternoon and tonight. A northerly
swell arriving tomorrow (Monday) and stronger winds will increase
the risk of rip currents and promote life-threatening rip currents
through at least late Wednesday. For more information and details
about the latest forecast please refer to the Surf Zone Forecast
(SRFSJU) and the Coastal Hazard Message product (CFWSJU).

&&


.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk from Monday morning through Wednesday
     afternoon for PRZ001-002-005-008.

VI...None.

AM...Small Craft Advisory until 6 PM AST Wednesday for AMZ711.

     Small Craft Advisory from noon Monday to 6 PM AST Wednesday for
     AMZ712.

     Small Craft Advisory from 6 PM Monday to noon AST Wednesday for
     AMZ716-723.

     Small Craft Advisory from noon Monday to noon AST Wednesday for
     AMZ741.

&&

$$

SHORT TERM/MARINE/BEACH FORECAST...YZR
AVIATION...YZR/RC
LONG TERM....DS
PUBLIC...ERG