499
FXCA62 TJSJ 060923
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
523 AM AST Thu Jun 6 2024

.SYNOPSIS...

Troughiness at different levels across the northeastern Caribbean
will continue to enhance shower and thunderstorms development
across the regional waters and portions of the islands through
today. A Saharan Air Layer will bring a drier airmass and dust
across the local area leading to hazy skies, mainly today and
Friday. Hot temperatures are expected throughout the weekend. The
next tropical wave with better potential of rain is expected by
next Tuesday into Wednesday.

&&

.SHORT TERM...Today through Saturday...

An elongated surface trough north of the islands extending into the
Central Atlantic combined with plenty of tropical moisture promoted
showers and thunderstorms across the local waters overnight. These
thunderstorms moved inland across portions of PR and the USVI,
producing periods of moderate to locally heavy rain. Skies were
variably cloudy, and the winds were mainly from south to southeast.

From now until this afternoon, a southerly wind flow will bring an
abundance of moisture over the islands. This, combined with an
elongated surface trough to the north, will likely result in showers
and thunderstorms near the islands. These conditions may sometimes
lead to heavy downpours, potentially causing ponding water in roads
and poorly drained areas and even urban or river flooding.

The high humidity combined with the expected maximum air temperature
will create heat levels that could affect most individuals sensitive
to heat, especially those without effective cooling and/or adequate
hydration. Therefore, a Heat Advisory is effective today, especially
between 10 AM and 5 PM AST. Additionally, a Saharan Air Layer will
spread from the east into the islands by mid-morning into the
evening, creating hazy conditions and slowly limiting rain activity.
However, the arrival of these suspended air particles may promote
the formation of robust thunderstorms, especially when the
concentrations are not high enough to suppress cloud development.

A more typical weather pattern with a combination of sunshine and
clouds may evolve from Friday into the weekend as moisture content
returns to typical values and the surface trough moves far from the
northeast Caribbean. However, the above-normal temperatures will
continue under the southeast winds, which may extend the heat spell.
Strong afternoon convection may also develop due to local effects,
excessive heat, and fluctuations in sea breeze. Additionally, the
warmer-than-normal sea surface temperatures will promote nighttime
convection across the surrounding waters, moving inland
occasionally.

&&

.LONG TERM...Sunday through Thursday...

A dryer and more stable weather pattern is expected to prevail
across Puerto Rico and the U.S. Virgin Islands during the
beginning of the long-term period as a deeply layered ridge sets
just east of the Leeward Islands and some Saharan Dust particles
will remain over the area. People will experience hazy skies and
sensible people with respiratory illnesses could still be
affected. The latest Precipitable Water (PW) models suggest values
decreasing to normal and even below normal climatological levels
for this time of the year, around 1.4 to 1.7 inches. Recent
guidance also shows dry air at the mid-levels of the atmosphere
and the 500 mb temperatures around -5 degrees Celsius, meaning
that if any rainfall activity does develop, it will not grow much
vertically, however, we cannot rule out the typical afternoon
convection across the islands, mainly over the western quadrant of
Puerto Rico during the afternoon hours due to diurnal heating and
local effects.

By Tuesday afternoon into Wednesday, a slight change in the weather
pattern is anticipated as patches of moisture associated with our
next tropical wave reach the island. That will result in better
chances of rain by midweek. On Thursday, a patch of dry air should
reach the islands again.

Overall, during the long term, we forecast mostly stable weather
conditions across the islands, with southeasterly to east-
southeasterly winds and moisture returning by Tuesday afternoon
into Wednesday. With this weather pattern, we anticipate warm
temperatures with the possibility that heat products like
advisories and warnings will be issued along the lower elevations
and urban areas. We encourage residents and visitors to stay
hydrated and updated with our latest weather forecasts.

&&

.AVIATION...

(06z TAFs)

We expect the arrival of SHRA/TSRA across the local flying area.
This could lead to brief periods of MVFR or brief IFR conditions
at local terminals, especially through this aft. Winds will be
predominantly from the SE/ESE at 5 to 10 kt, then between 10-15 kt
after 06/13z, with higher gusts (especially near TSRA) and sea
breeze variations. Hazy skies will be possible, especially by this
afternoon, as suspended dust particles from the Sahara desert
filter from the east over the region, but with P6SM.

&&

.MARINE...

A surface high pressure north of the area will slowly move
eastwards and build into the central Atlantic by the weekend. A
surface trough will remain mainly north and west of the area. In
response, light to moderate east to southeast winds will prevail
across the local waters. Isolated thunderstorms across the waters
and local passages are possible through today, then more stable
conditions are anticipated throughout the weekend. The next
tropical wave with better potential for squally weather is
expected by early next week.

&&

.BEACH FORECAST...

Today, mainly low risk of rip currents across Puerto Rico,
Vieques, Culebra, St Thomas, and St John, while a moderate risk
across beaches of St Croix. Mainly low risk should prevail throughout
the weekend. For more information and details about the latest
forecast please refer to the Surf Zone Forecast (SRFSJU).

&&

.SJU WATCHES/WARNINGS/ADVISORIES...

PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for PRZ001-005-008-010.

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

AM...None.


&&

$$

SHORT TERM/AVIATION...CAM
LONG TERM/MARINE....YZR