175
FXCA62 TJSJ 122030
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
430 PM AST Sun May 12 2024

.SYNOPSIS...
A more seasonal weather pattern is forecast through the period.
As winds become more easterly over the next few days, the
heaviest rain is expected across the interior to western sections
of PR. Temperatures along the coast and in urban areas this week
can reach the upper 80s to mid 90s today, with heat indices that
may exceed 102 degrees Fahrenheit (localized areas possibly
experiencing 108-110 degrees). Marine and beach conditions this
week are the calmest they have been in a while with a low risk of
rip currents for most of the week.


&&

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

Expect a typical seasonal weather pattern with
afternoon convective activity due to diurnal heating and local
effects. With an upper- level jet streak situated to the north
through tomorrow morning and moisture levels remaining slightly
elevated, passing showers are possible through the night.

As the jet streak gradually moves northward starting tomorrow, a
mid- level high pressure will extend into the northeastern
Caribbean, establishing a trade wind cap inversion and bringing
drier conditions aloft. Consequently, precipitable water values
will decrease, eventually falling to the lower end of typical
thresholds as moisture becomes confined below the 700 mb layers.
Despite conditions becoming less conducive to convective
development and a gradual decrease in moisture, afternoon showers
with possible isolated thunderstorms on Monday and Tuesday are
still likely, with less area coverage and intensity each passing
day, possibly generating limited flooding risk. As winds become
more from the easterly and increase to 10-15 mph early next week,
the focus of the afternoon activity will shift to portions of the
western interior to western Puerto Rico.

Each afternoon temperatures along the coast and in urban areas
today may rise to the upper 80s to mid-90s, while higher
elevations could experience highs in the upper 70s to mid- 80s. Heat
indices may exceed 102 degrees Fahrenheit, with localized areas
possibly experiencing 108-110 degrees. Lingering saharan dust is
present in the area causing slightly hazy conditions.

&&

.LONG TERM...Wednesday through Sunday...
/from previous discussion/

Precipitable water (PWAT) values should remain at normal values
for this time of the year, between 1.5 to near 2.0 inches, during
the period, as patches of moisture advect into the region. Model
guidance seems to have backed off on moisture significantly
increasing by the end of the workweek, now showing only patches of
high end seasonal PWAT reaching the islands. For at least the
start of the period, NASA aerosol optical thickness (AOT) suggests
lingering Saharan dust particles to start the period. A mid-level
ridge will exert its influence over the region to start the
period, promoting more typical weather with afternoon convection
due to diurnal and local effects. Model guidance now suggests an
upper trough moving north of the islands from the northwest by
Friday and Saturday. Most available moisture should reach up to
850 to 800 mb for the period. Light to moderate easterlies are
forecast through the period as a surface high moves into the
western to central Atlantic. Limited to possibly elevated Heat
Risk, especially during the daily maximum heating, will persist
across several lower elevation sectors of the islands where no
significant rain is observed. This diurnal heating, along with
local effects and sea breeze convergence will continue to promote
up to strong afternoon convection, steered by easterly winds. This
will promote convective activity mainly over sectors of the
interior to western half of the Puerto Rico and downwind of the
local islands. Early morning and overnight passing showers are
also forecast across windward sectors of the islands along with
patchy fog over areas of the interior.


&&

.AVIATION...
(18Z TAFS)

Mainly VFR conds expected to prevail across all terminals during the
next 24 hours. SHRA and TSRA expected to develop over the Cordillera
Central and TJBQ through 12/23Z. VCTS/VCSH expected for the
TJBQ/TJPS terminals after 12/18Z may result in brief MVFR cigs. VCSH
may affect the TIST/TISX terminals after 12/23Z, with minimal
impacts to operations. Light to calm and variable winds from the SE
btw 10-12 kts, decreasing to less than 5 kts overnight. Winds are
expected to increase btw 10-12 kts with higher gusts by 13/13Z.


&&

.MARINE...

Seas will be favorable for small craft through at least Thursday. A
surface high pressure across the central Atlantic and a low in the
western Atlantic will allow light to moderate east winds to prevail
tonight. As another high moves into the western Atlantic winds will
be light to moderate easterlies through the rest of the period.
Afternoon convective activity could move from the islands towards
nearby waters.


&&

BEACH FORECAST...

Low Risk of Rip Currents for most of the week. However, they
occur most often at low spots or breaks in the sandbar and in the
vicinity of structures such as groins, jetties and piers.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

CAM/MMC/RC