548
FXCA62 TJSJ 220756
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
356 AM AST Sat Jun 22 2024

.SYNOPSIS...
A summer-like pattern will persist for the weekend across the
islands, with passing showers early in the day, and afternoon
convection for the interior and western Puerto Rico each day. A
tropical wave will approach the area on Monday, followed by
Saharan dust. Hot temperatures will prevail for the forecast
period.

&&

.SHORT TERM...Saturday through Monday...

Surface ridging continues to dominate the Atlantic Basin, allowing
moderate easterly flow to prevail across the lower levels through
Sunday. This trade wind pattern will stream humid air masses
across the region, allowing windward showers and afternoon
convection to occur. Under a weak ridge across the mid to upper-
levels, local effects and diurnal heating will provide enough
instability to bring heavy rainfall during the afternoon hours for
western Puerto Rico where flooding and strong thunderstorms
remain possible.

On Sunday, lower level winds start to veer, becoming southeasterly
as the surface high in the Atlantic becomes more centered at about
45W longitude and as a tropical wave begins to move into eastern
Caribbean Basin. Weather conditions are likely to deteriorate
Sunday Afternoon onward as this tropical wave moves through the
area on Monday. Expect a rapid increase of passing showers Sunday
night into Monday morning, then heavy convection during Monday
afternoon for multiple sections of the islands. Breezy conditions
are forecast to occur as well, which will bring squally weather at
times with strong thunderstorms. Northwestern Puerto Rico may see
the heaviest rainfall during Monday afternoon, however
southeastern PR may see some impressive thunderstorms capable of
bringing lots of rain.

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

After the tropical wave departs, a surface high pressure will take
control of the atmospheric conditions. First, this feature will
drive the trade winds from the southeast, and will tighten the
pressure gradient, with surface speeds around 20 knots. Also, a
trade wind cap inversion will form at around 800 mb, trapping all
the available moisture below this level. Moderate to strong
concentrations of Saharan dust may arrive too, with hazy skies and
little precipitation expected through at least early Thursday. This
conditions, however, will make temperature soar, with very hot
conditions expected to return these days.

By Thursday, as an induced surface trough (more evident in the 700
mb pressure field) approaches, the winds are expected to shift from
the northeast at these heights, and the trade wind cap will weaken.
Instability should be enough to fire up showers and thunderstorms
for the interior and western portions of Puerto Rico, with an
elevated risk for urban and small stream flooding, and lightning.
Also, by the end of the week, an upper level trough will approach
the Leeward Islands. This trough is not expected to affect the local
islands directly, but it will allow for better shower and
thunderstorm production each afternoon across the usual interior and
western Puerto Rico. Shower activity will become more frequent too
for eastern Puerto Rico and for the Virgin Islands. Saharan dust
will not completely go away, but concentrations are expected to be
lower. This low concentrations of dust could contribute to enhance
the frequency of the lightning activity within the thunderstorms.


&&

.AVIATION...
(06Z TAFs)

Mainly VFR conditions expected to prevail through the forecast
period with periods of reduced VIS and low ceilings possible during
the afternoon. SHRA will continue across the region, impacting the
USVI terminals and TJSJ through the day. Widespread SHRA and
isolated TSRA expected after 15Z, effecting also TJPS and TJBQ.
Winds will be out of the E at 14-18 kts, with gusts around 25 kts
from 13-22z.

&&

.MARINE...
A surface high pressure over the central Atlantic will promote
moderate to locally fresh easterly winds through the rest of the
week. Trade wind showers will move across the regional waters from
time to time. The next tropical wave will approach the local islands
by the beginning of the next workweek.

&&

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

$$

SHORT TERM...RC
LONG TERM....ERG