044
FXCA62 TJSJ 150955
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
555 AM AST Thu Aug 15 2024

.SYNOPSIS...
Hurricane Ernesto now located north of 23N, and over 300 miles northwest
of San Juan, will maintain moderate southerly wind flow across the area
today into Friday as it moves north northwestward and farther away
from the region. Overall weather conditions are forecast to gradually
improve throughout the day with winds becoming more southeasterly then
easterly by Friday and into the weekend. A low to moderate concentration
of Saharan dust will arrive and spread across the region later today
and into the upcoming weekend along with a weak easterly wave which
will arrive across the local area late Friday into Saturday. Overall
hot and humid conditions will promote excessive heat conditions for
some coastal and urban areas for the next several days.

&&

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

Current Satellite derived precipitable water (PWAT) indicate remnant
moisture from the tail of the now far northwest Ernesto maintaining
up to 2.0 inches (borderline above normal values for this time of
the year) over the region. Rainfall yesterday have kept several
rivers under a Flood Advisory overnight, with the last ones, Rio
Culebrinas, Rio Grande de Manati and Rio Guanajibo being under a
Flood Advisory until early this morning. Light showers have
persisted over interior Puerto Rico overnight as southerly flow
keeps bringing moisture over the area. Lows ranged from the mid to
upper 70s over north-central to northwestern, and eastern interior,
PR to the low 80s across most other coastal areas of the islands.
Only isolated sectors of interior PR had lows in the upper 60s and
low 70s. As Ernesto continues to move further away from the region,
moisture across the islands will gradually decrease today to normal
PWAT values. PWAT values will remain at normal values, with even
drier patches of air arriving at times. Ridging trough at least
700mb will move into the region during the period, promoting more
drying and subsidence. Southerly to southeasterly flow will dominate
the period. Winds from this direction tend to promote warmer than
usual conditions. An increased heat risk will be present today as
heat indices elevate to above 108-110 degrees at coastal and lower
elevation areas of the islands. Citizens and tourists are encouraged
to practice heat safety measures as we end the workweek. Passing
showers will affect windward sectors at times with convective
activity developing due to diurnal heating, sea breeze convergence
and local orographic effects over sectors of the interior and
northwest, today and tomorrow. Data from the Puerto Rico Landslide
Forecast Network shows high levels of soil saturation. With these
saturated soil conditions and lingering moisture during the rest of
today and the next few days, any additional shower development
across these areas can promote ponding of water on roads and minor
flooding as well as mudslides in areas of steep terrain. By the
start of the weekend, a weak tropical wave will increase instability
and increase PWAT values to normal/above normal values once again.
Saharan dust will also be present during the short term period,
producing somewhat hazy skies.

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

A surface high building across the area and the northeastern Caribbean
will spread further west northwest Across west and southwest Atlantic
increasing the easterly trade winds. An tropical wave is forecast
to cross the eastern Caribbean Sunday through Monday and will
bring a quick surge of moisture and increase passing showers to
the region along with another low to moderate concentration of
Saharan dust. By then winds are to become more east southeast and
thus maintain hot and humid conditions. Better moisture is still
forecast to move across the region accompanying another tropical
wave by the middle of the following week will bring another surge
of additional moisture and increase the potential for enhanced
shower activity across the area. Precipitable water values will
range between 1.5 to 2.0 inches with a prevailing east to southeast
wind flow through the period. Therefore a more typical weather pattern
will prevail for Puerto Rico and the U.S. Virgin Islands except for
the occasional patches of trade wind moisture forecast to cross
the region from time to time accompanying the moderate easterly
trades. Therefore periods of passing overnight and early morning
showers will persist over the coastal waters and eastern Puerto
Rico and the U.S. Virgin Islands, followed by afternoon showers
and thunderstorms mainly over western and the interior parts of
the island each day. For the U.S. Virgin Islands periods of isolated
to scattered showers are expected with limited amounts of rainfall
accumulations expected at this time.

&&

.AVIATION...
(06Z TAFS)

Mainly VFR conditions across the terminals. S-SE winds up to around
15 kts with higher gusts will be present, decreasing after 15/22Z.
Afternoon VCSH/Iso-VCTS starting over the interior can affect TJPS
around 15/17Z-22Z. Light Saharan dust will also promote somewhat
hazy skies.

&&

.MARINE...Hazardous seas will slowly diminish as Hurricane Ernesto
pulls farther away from the region. Therefore small craft advisories
are not expected after noon today and for the rest of the week. However
choppy conditions will continue due to the moderate to locally fresh
south to southeast winds. Nevertheless small subsiding swell from
Ernesto may continue to arrive across the local Atlantic waters through
the upcoming weekend. Showers and isolated thunderstorms will also
remain possible over portions of the local waters and passages
especially during the late afternoon and evening hours.

&&

.BEACH FORECAST...Rip current risk will remain moderate for all
beaches Today. Due to the swell returning from TC Ernesto, the
rip current risk will remain moderate for some northern beaches
on Friday and through the upcoming weekend.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for PRZ001-002-005-008-010-012-013.

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

AM...Small Craft Advisory until noon AST today for AMZ711-741.

&&

$$

SHORT TERM...MRR
LONG TERM....RAM
AVIATION...MRR