365
FXCA62 TJSJ 150920
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
520 AM AST Sat Jun 15 2024

.SYNOPSIS...
Another warm day is forecast for the northern and northwestern
coastal areas today, where heat indices could reach 100 to 112
degrees Fahrenheit. Given these expected conditions, an Excessive
Heat Warning is in effect from 10 AM to 6 PM and a Excessive Heat
Advisory for the same time-frame for Culebra, Vieques and the
U.S. Virgin Islands. Another warm day is forecast for tomorrow
where a Excessive heat Watch remain in place for most of the
northern coastal area. Please follow the recommendations from the
local health department to avoid heat exhaustion. Additionally,
convection is expected as plenty of moisture remains in the area,
brought in by the southeasterly wind component.


&&

.SHORT TERM...Today through Monday...

A surface trough will continue to exit the region today with
trailing moisture expected to affect the local islands and coastal
waters during the rest of the morning hours, steered by the
prevailing southeast low level winds.  Recent Doppler weather radar
VAD wind profile suggest winds veering southeast-south below 700
millibars favoring a warm moist environment in the low levels. Mid
to upper levels suggests the region remains on the subsident side of
the trough lingering east of the region, while an upper ridge will
hold just to our west. Expect this overall pattern to persist
through the weekend with a light to moderate plume of Saharan Dust
and suspended particulates expected to continue crossing the region
today through Sunday. Although the highest concentration of dust
should move just south of the region, the low level wind flow will
bring sufficient dust for slightly hazy conditions especially later
today and on Sunday. Although drier air will filter in across the
region today along with the Saharan dust, there will enough moisture
available to aid in the development of afternoon showers and
isolated thunderstorms each day. With fairly light winds and local
sea breezes, most of the expected rainfall should be focused across
eastern, central and northwest sections of Puerto Rico steered by
the southeast wind flow.

The suspended Saharan dust particulates, along with the warm
southerly flow and presence of the mid to upper level ridging will
continue to favor subsidence and support above normal daytime high
temperatures in the low 90s especially along the north and west
coastal areas. That said, maximum heat indices are expected to
exceed 100 degrees once again, resulting in excessive heat impacts
especially along the west, north and east coastal and urban areas.
These conditions will also remain likely on Sunday. Therefore
excessive heat warnings and advisories will be issued for portions
of the islands today and a Heat Watch will remain possible for
Sunday. Please refer to the latest Non-Precipitable Weather
Message(NPWSJU) issued by WFO SJU PR for additional information on
these heat impacts.

.LONG TERM...Tuesday through Saturday...

A deteriorating weather trend is forecast for the first part of
the long-term period. A trough will build just over the western
Atlantic at the upper and mid-levels. The presence of the mid- to
upper-level feature will decrease the 250 MB height and turn the
temperatures at 500 MB colder, ranging from -7 to -8 degrees. This
increases the potential for more widespread lightning activity on
Tuesday into Wednesday. According to the global model guidances
(GFS and ECMWF), surface conditions will also be favorable for
shower activity due to plenty of tropical moisture embedded in the
east-southeasterly wind flow across the region. Given the
expected conditions from Tuesday into Wednesday, the islands will
experience passing showers in the morning hours over the eastern
sections, the U.S. Virgin Islands, and the local waters, followed
by widespread shower activity across the western interior. So far
today, the rainfall threat is mostly concentrated across the
western interior, with ponding of water in roadways and poor
drainage areas. From Thursday into Saturday, plenty of surface
moisture will continue to stream across the local islands, keeping
the potential for convection in the afternoon, especially across
the mountains and the western interior. Although plenty of
moisture will remain in place, more stable conditions will be
present at the upper level, provided by an upper-level ridge.

A similar temperature pattern is expected across the islands by the
first part of the long term. According to the model guidances,
925 MB temperature, the trend calls for warmer conditions,
resulting in heat indices rounding 108 to 112 F degrees. Residents
and visitors are urged to stay informed of possible advisories or
warnings due to Excessive heat.

&&

.AVIATION...
(06Z)
SFC trough crossing the region will bring wdly SCT SHRA with SCT
ocnl BKN cld lyrs nr FL025...FL050..FL080 over regional waters and
en route btw islands. VFR conds will prevail at all terminals but
Tempo 4-5SM psbl with SHRA at TJSJ/TIST/TISX til at least 15/12Z,
Brief MVFR and Mtn top Obscr psbl ovr Eastern PR due to low clds
and -SHRA. SFC wnd calm to lgt/vrb but with a light(5-15 KTS)
southerly component in the low levels BLO FL100. SFC wnd bcmg
mainly fm the SE around 10 kts aft 15/14Z.

&&

.MARINE...

A broad surface high pressure over the eastern Atlantic extending
into the Central Atlantic interacting with an induced surface
trough just north of the CWA will continue to promote a light to
moderate south-southeasterly. Under this pattern and tropical
islands, the local waters will experiment with seas up to 5 feet
and winds up to 15 knots. Isolated to moderate showers with
thunderstorm activity would result in localized hazardous marine
conditions. There is a low risk of rip currents for all the
exposed coastal beaches in the region.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Excessive Heat Warning from 10 AM this morning to 6 PM AST this
     evening for PRZ001-005-008-010.

     Excessive Heat Watch from Sunday morning through Sunday
     afternoon for PRZ001-002-005-008-010-012-013.

     Heat Advisory from 10 AM this morning to 6 PM AST this evening
     for PRZ002-012-013.

VI...Excessive Heat Watch from Sunday morning through Sunday
     afternoon for VIZ001-002.

     Heat Advisory from 10 AM this morning to 6 PM AST this evening
     for VIZ001-002.

AM...None.
&&

$$

SHORT TERM...RAM
LONG TERM....LIS
AVIATION...RAM