124
FXCA62 TJSJ 290834
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
434 AM AST Mon Apr 29 2024

.SYNOPSIS...

The surface high pressure over the western Atlantic will continue
to promote breezy northeasterly winds through at least midweek.
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 a mid to upper level trough lingers
over the western Atlantic and lighter east to southeast winds
return.

&&

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

Showers persisted through the early morning hours across portions of
northern and eastern PR and across the USVI. The Doppler radar
estimated between 1 and 2 inches of rain over Fajardo and Luquillo.
Minimum temperatures were from the mid-to-upper 70s across coastal
areas to the mid-60s across the higher elevations. Wind gusts were
up to 20-25 mph with the showers.

A strong surface high-pressure moving off the eastern coast of the
U.S. will move slowly towards the Central Atlantic during the next
few days. This system will bring slightly drier air to the region,
but the amount of precipitable water (PWAT) across the Caribbean
will still be within typical seasonal values. The surface high will
promote breezy conditions with moderate to fresh northeasterly winds
through at least Tuesday, then winds will shift from the east to
southeast and become light to moderate on Wednesday as the surface
high weakens. Therefore, we expect an advective pattern during the
nights with cooler air moving over warm waters and bringing showers
across portions of the USVI and along the north and eastern half of
PR, followed by diurnally induced afternoon convection over portions
of the interior and south/southwest PR each day.

Wednesday looks to be the wettest day of the short-term period as an
upper-level trough approaches the area from the west and an induced
surface trough develops over the northeastern Caribbean. This will
enhance shower and thunderstorm development across much of Puerto
Rico. Urban and small stream flooding and mudslides in areas of
steep terrain are possible.

High temperatures will remain in the mid-to-upper 80s along the
coastal and urban areas and in the mid-to-upper 70s along the
mountains and valleys. Minimum temperatures will range from the
upper 70s to low 80s across coastal areas to the mid-60s in the
higher elevations.

&&

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

The inherited forecast remains unchanged. Recent model guidance
suggests a mid-to-upper-level trough developing and staying
nearly stationary over the west to southwestern Atlantic, at least
through the long-term period. From Thursday onwards, expect the
winds to become lighter as the surface high pressure north of the
area continues to weaken. By Thursday, remnants of an old frontal
boundary will reach the island from the northeast and merge with a
trough or perturbation over the northeastern Caribbean. This will
lead to unstable and wetter weather conditions across Puerto Rico
and the U.S. Virgin Islands, with possible flooding impacts and
mudslides in areas of steep terrain across Puerto Rico. At this
time, Precipitable Water (PW) models suggest values above two
standard deviations and, therefore, above the normal
climatological levels for this time of the year. We anticipate
active afternoons during the long-term period, 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 and 106 degrees on Friday and Saturday
before the onset of afternoon convection. Overall, an unstable and
wetter patternis expectedto evolve over thelong-term.

&&

.AVIATION...
(06z) TAFS

Although VFR conds should prevail through most of the period, trade
wind SHRA may cause brief MVFR cigs at TJSJ/TIST/TISX/TJBQ at times.
Tempo MVFR conds are possible at TJPS btw 29/18-22z due to TSRA. NE
winds at 15-20 kt with stronger gusts near 30 kt during the day.

&&

.MARINE...

A sub tropical high pressure across the western Atlantic will
promote moderate to fresh trade winds through at least mid-week. We
expect hazardous seas for small craft operators due to confused seas
associated with the increasing winds and a northeasterly swell
spreading across the local waters.

&&

.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 through Wednesday afternoon for PRZ001-002-
     005-008.

     High Rip Current Risk from this evening through Wednesday
     afternoon for PRZ010-012.

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

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

     Small Craft Advisory from 6 PM this evening to noon AST
     Wednesday for AMZ716-723-742.

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

&&

$$

SHORT TERM...DS
LONG TERM...MMC
AVIATION...DS
MARINE/BEACH FORECAST...MMC