277
FXCA62 TJSJ 172027
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
427 PM AST Mon Jun 17 2024

.SYNOPSIS...

Surface high pressure over the central and northeast Atlantic and an
elongated area of low pressure west of the region, will induce a weak
trough over the area to promote light east southeast winds through
Tomorrow. Following this high pressure will build north and east
of region thereafter promoting an increase in the easterly winds.
The upper ridge will continue to erode as a trough deepens west of
the region. Moist and unstable condtions will continue through
mid week, with showers and isolated thunderstorm likely each day,
especially over the central interior and northwestern quadrant of
Puerto Rico.

&&

.SHORT TERM...Tonight through Wednesday...

Showers and isolated thunderstorms will persist into the night
before clearing out over land, with eastern Puerto Rico having the
chance of passing showers into the morning hours. A surface induced
trough north-northeast of the area and high pressure across the
central Atlantic will maintain an easterly to southeasterly flow
throughout the short term, combining with moist air from arriving
tropical waves to continue the trend of hot days with showers
including convection during the afternoon hours. In the mid to upper-
levels low pressure begins to establish across the western Atlantic
as a surface low builds. The proximity of this upper trough
throughout the next few days will enhance rainfall in combination
with the surface features moving in from the eastern Caribbean.

On Tuesday, a tropical wave is forecast to arrive late in the day
from the southeast brining instability across the lower-levels as
it matches up with the divergent side of the upper-level trough
just west of the region with the axis over Hispaniola, resulting
in an increase of moisture across the lower levels and colder
temperatures in the 500 MB. The Glvez-Davison Index (GDI) shows
potential for daily isolated to scattered thunderstorm activity.
Although all the variables favor a wet pattern, the NASA Goddard
Earth Observing System Model V5 shows a decent pulse of Saharan
Air Dust across the region early Wednesday, resulting in hazy
skies and muggy conditions across the region.

Each day the heaviest rainfall is forecast across the interior to
western sections of Puerto Rico due to local effects and diurnal
heating, urban flooding is possible with the heaviest rainfall. And
yet again, daytime high temperatures are forecast to be in the upper
80s to low 90s especially along the north and west coastal areas.
This along with the humid conditions and southeasterly winds will
again favor maximum heat indices to exceed 100 degrees tomorrow.
Please refer to the latest Non- Precipitable Weather Message(NPWSJU)
issued by WFO SJU PR for additional information on the expected heat
impacts.


&&

.LONG TERM...Thursday through Monday...
/from previous discussion/

Moist and unstable weather conditions are expected to continue
through at least the early part of the period as a deepening
upper- level trough with the axis over Hispaniola west of the
region,will linger and provide good ventilation and a divergent
pattern aloft. This along with good tropical moisture convergence
produced by the prevailing and moderate east to southeast and a
passing tropical wave, will maintain good potential for shower and
thunderstorms development at least through Friday and moisture
trailing the wave will combine with the instability aloft and good
daytime heating to maintain moderate to high potential for
afternoon and early evening convection. Based on the most recent
guidance and Glvez- Davison Index (GDI)product, the potential for
isolated to scattered thunderstorm will continue through Friday.
Overnight and afternoon showers will be likely with a limited
flood threats across portions of the islands each day. Hazy skies
will continue at least through Thursday due to some lingering
Saharan Dust with improving conditions by Friday and into the
weekend.

Over the following weekend and through Monday, a broad surface
high pressure will again spread across the Central Atlantic and
Eastern Atlantic result in increasing east to southeast trade
winds and variable weather conditions. Under the expected low
level wind flow, plenty of surface moisture will continue to stream
across the islands and coastal waters, thus maintaining the potential
for passing showers overnight and afternoon convection each day.
This expected activity should be focused particularly across the
central interior and west sections of Puerto Rico,while the U.S.
Virgin Island can expect afternoon showers mainly on the west-end
and downwind of the islands with fewer shower activity elsewhere
from time to time.

A similar and slightly above normal temperature pattern is expected
to continue across the islands at least through the early part of
the long term. Model guidance remains persistent in maintaining overall
hot and humid conditions although the easterly are expected to increase
during the latter part of the period. Residents and visitors are
urged to stay informed of possible advisories or warnings due to
excessive heat conditions.

&&


.AVIATION...
(18Z TAFS)

Brief periods of MVFR conditions will remain possible at JSJ and JBQ
in TSRA/SHRA through at least 17/22z. Aft 17/22z VFR conditions will
prevail at all TAF sites. Winds are light from the E-SE, and more
VRB after 17/22z.

&&

.MARINE...

Surface high pressure over the Atlantic and the proximity of an
induced trough across the region will promote light to moderate
east to southeast winds today through Tuesday. Passing showers
and isolated thunderstorms will continue to affect the coastal
waters and local passages resulting in localized hazardous marine
conditions especially over the offshore Atlantic and Caribbean
waters and between eastern Puerto Rico and the U.S. Virgin Islands
during the early morning hours and on the west coastal areas Turin
the afternoon hours. The easterly winds are forecast to increase
to moderate to locally fresh by late Wednesday and through the
rest of the work week.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...

VI...

AM...None.
&&

$$

CAM/YZR/RC