Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 042038
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
438 PM AST Mon Jul 4 2022

.SYNOPSIS...

The easterly winds will promote passing showers overnight and in
the morning across the windward sections of Puerto Rico and the
U.S. Virgin Islands daily. Each afternoon expect convection across
the interior and western municipalities of Puerto Rico and
downwind from the Virgin Islands and El Yunque. African dust
particles will be present and should increase by the end of the
workweek. Another tropical wave will move into the Caribbean Sea
by the weekend.

&&

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

This afternoon convection should continue through sunset, then
will leave clear skies across most of the islands. After that, we
expect calm weather from tonight to tomorrow morning. Nighttime
cooling will promote lows in the mid and upper 70s across coastal
areas to the low 70s or upper 60s across mountains and valleys.
Traces of African Dust Particles will remain across the islands
without impacting local visibilities.

A surface high pressure over the Central Atlantic will induce an
east to east-southeast wind flow across the islands. This wind
flow will result in normal to above-normal high temperatures
across the urban and coastal areas; combined with the available
moisture; it will result in heat indices equal to or greater than
100 degrees Fahrenheit.

A Tropical Upper Tropospheric Trough (TUTT) will linger aloft near
the islands. The TUTT aloft will induce perturbations in the wind
flow, promoting an advective summer pattern across the local
waters during the overnight and morning hours. Therefore, expect
passing showers across these areas each day. Then, the proximity
of this TUTT combined with local effects, sea breeze variations,
and diurnal heating will aid in the formation of showers and
thunderstorms across the interior and western sections of Puerto
Rico and downwind from the Virgin Islands and El Yunque. A weak
tropical wave will reach the local region by mid-week, increasing
the potential for the formation of stronger showers and
thunderstorms.

.LONG TERM...Thursday through Sunday...from prev discussion...

A strong high pressure centered across the north Atlantic will
remain the dominant feature at the surface, leading to a generally
east to southeast wind flow at around 10-20 mph through the
cycle. A mid-to-upper level low to our west will maintain
favorable conditions for deep convective development through the
end of the workweek before a mid-level high briefly leads to drier
air entrainment and development of the trade wind cap inversion
on Saturday. While the entrance of drier air may lead to mainly
fair weather conditions on Thursday and early Friday into Friday
night, with model-estimated precipitable water values below-normal
seasonal levels as low as 1.4 inches, a weak tropical wave
streaming across the Caribbean Sea and south of the local islands
and fast-moving easterly perturbations embedded in the general
flow will bring moisture to normal seasonal levels at about 1.8
inches by Friday morning and Saturday morning into Saturday
evening. Despite variations in moisture content and mid-to-upper
level conditions, local and diurnal effects will support a typical
seasonal pattern each day, with the highest impacts expected from
afternoon convective development across the interior to western
portions of Puerto Rico during the wettest periods. Saharan Dust
concentration will maintain hazy conditions, especially during the
driest periods.

By Sunday and continuing early next week, the passage of a
tropical and associated trailing moisture will lead to above-
normal seasonal moisture levels as high as 2.2 inches. If this
scenario materializes under the influence of yet another mid-to-
upper level trough to the northwest, the resulting moderate to
heavy rains could enhance the potential for flooding across the
local islands. Although this forecast has low to medium
confidence, given the event`s timing far out in the cycle, model
guidance has remained relatively consistent during the last few
solutions.

&&

.AVIATION...

VFR conditions will prevail thru the fcst prd. However, SHRA
pushed by the easterly wind flow will sometimes move across local
terminals. Afternoon convection will slowly dissipate by this
evening (around 05/00z), leaving mostly clear skies overnight.
SHRA/TSRA will develop across the Cordillera Central and downwind
from El Yunque/St Croix/St Thomas, tomorrow, btwn 05/17-23z. Winds
will become calm to light/VRB aft 04/23z, returning from the
E-ESE at 15-20 kt with higher gusts/sea breeze after 05/13z.

&&

.MARINE...

A surface-high pressure across the Atlantic Ocean will promote a
moderate to locally fresh east to east-southeast wind flow across
the local waters. This wind flow will promote choppy seas up to 6
feet across the local waters.

Beachgoers, there is a moderate risk for most of the local
beaches. The risk of rip currents is high from Aguadilla to
Barceloneta until tomorrow morning.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  77  89  77  90 /  30  40  50  40
STT  81  89  82  89 /  30  30  50  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through late tonight for North Central-
     Northwest.

VI...None.
AM...None.
&&

$$

SHORT TERM...CAM
LONG TERM....MRR
PUBLIC DESK...MM


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