National Weather Service Today's Weather Impact Levels

959
FXCA62 TJSJ 270913
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
513 AM AST Sat Jul 27 2024

.SYNOPSIS...

Hot and hazy skies due to a strong Saharan Air Layer will prevail
through at least the weekend. Shower and thunderstorm activity is
expected to increase by next week, particularly by mid-week as a
vigorous tropical wave approaches the area.

&&

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

Hazy skies due to a strong Saharan Air Layer will prevail through at
least early Sunday. Hot temperatures are expected to continue today
with heat indices expected to range from 106 to 112 degrees
Fahrenheit, mainly along the lower elevations of western, southern
and northern Puerto Rico, and St. Croix. Therefore, a Heat Advisory
(NPWSJU) was issued across these areas, and could likely be issued
once again on Sunday and Monday as the SAL exits the region and
dewpoints increase. Although shower activity will be limited in
general, diurnally induced streamers developing off the USVI and
smaller islands and showers with possible isolated thunderstorms
could still develop during the afternoons over portions of
west/southwest PR.

On Monday, a TUTT induced trade wind perturbation or weak trough is
expected to move from the east and bring an increase in moisture
content. Precipitable water content could increase between 1.75-2.00
inches by Monday afternoon. Therefore, showers will increase in
coverage as well as the potential for better organized afternoon
convection over the interior and western Puerto Rico. Urban and
small stream flooding can be expected with this activity. Drier
conditions and hazy skies will follow quickly by Monday night as a
weak Saharan Air Layer filters from the east.

.LONG TERM...Tuesday through Saturday

A seasonal weather pattern will prevail on Tuesday, with slightly
below-normal to near-normal moisture levels across the forecast
area. This will bring occasional trade wind showers over windward
coastal areas during the morning hours and a few isolated
thunderstorms across western Puerto Rico.

Afterward, forecast details become more complicated as several
features will reach the northeastern Caribbean by mid-week.
Troughiness aloft will promote favorable weather conditions
conducive to convective development. At low levels, a wind surge
will first reach the local islands by early Wednesday, bringing
gusty wind conditions and squally weather to the region. From the
rest of the day through Thursday, a vigorous tropical wave behind
the wind surge will increase moisture content to well above normal
levels, in some instances reaching close to 2.40 inches. The
National Hurricane Center is currently monitoring the tropical wave
with a low formation chance in the next seven days. However,
uncertainty remains as some global models now predict the tropical
wave developing after it passes the CWA. The timing also differs
between models, with the ECMWF forecasting the tropical wave
arriving and exiting the region earlier than the GFS model.

Adding to this complex scenario is the presence of another Saharan
Air Layer event engulfing this tropical wave. The Saharan dust
particulates could be another limiting factor for shower and
thunderstorm activity. The rest of the week will depend on the
behavior of this tropical wave. The GFS model predicts lingering
moisture lasting through the weekend, potentially prolonging the wet
and unstable weather period.

Forecast confidence is low regarding the impact of this tropical
wave on the forecast area for next week. Therefore, continue to
monitor the forecast, as slight deviations in the tropical wave`s
path and intensity could change the expected impacts across the
local islands. Regardless of the outcome, we can expect a shift in
weather conditions with increased instability and an elevated
flooding threat. This could potentially bring heavy rain, frequent
lightning, and gusty winds. Quick river rises and landslides
cannot be ruled out as this tropical wave crosses the northern
Caribbean.


&&

.AVIATION...
(06Z TAFs)

Mainly VFR conditions expected to prevail across all terminals thru
the next 24 hours. HZ due to Saharan dust may reduce visibilities
around 6SM through the forecast period. East to northeast winds
increasing at 15-20 kts, with stronger gusts and sea breeze
variations aft 27/14Z. -RA/VCSH expected early in the morning at
TJSJ/TJBQ, and btw 27/18z-22z at TJPS.


&&

.MARINE...

Surface high-pressure located in the central Atlantic will continue
to support moderate to locally fresh easterly winds and choppy seas
for small crafts over the next few days. A strong Saharan dust event
will continue to affect the local islands at least until early
Sunday, resulting in hazy skies and limiting shower activity.
By mid-week of next week, a vigorous tropical wave will promote
shower and thunderstorm activity across the regional waters along
with hazardous seas.

&&

.BEACH FORECAST...

Increasing winds this weekend into early next week will promote
moderate risk of rip currents for north- and east-facing beaches.
A vigorous tropical wave will reach the local islands by mid-week
of next week. This will increase shower and thunderstorm activity
across the area. Gusty wind conditions could increase rip current
risk to high in some beaches as well.



&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for PRZ001-003-005-007-008-010-011.

VI...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for VIZ002.

AM...None.
&&

$$

SHORT TERM/AVIATION...DSR
LONG TERM/MARINE/BEACH...CVB

NWS SJU Office Area Forecast Discussion