623
FXCA62 TJSJ 162049
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
449 PM AST Tue Jul 16 2024

.SYNOPSIS...

The weather conditions will continue to be influenced by an upper
level low and associated surface trough until Wednesday. A strong
Saharan Air Layer with Saharan dust and stronger trades will
dominate the local conditions through the end of the workweek. A
tropical wave with good moisture content will reach the area on
Saturday.


&&

.SHORT TERM...Today through Thursday...

Partly cloudy skies were observed across the islands today. A TUTT
low and associated surface trough over the eastern Caribbean
produced showers and thunderstorms across portions of the regional
waters and islands. The Doppler radar estimated just under 3
inches of rain in Arecibo. Maximum temperatures were from the
upper 80s to mid 90s across coastal areas to the mid 70s across
the higher elevations. Heat indices between 108F-116F were
observed across the lower elevations of northern and southwestern
Puerto Rico. Winds were from the east to southeast up to 18 mph
with higher gusts at times.

The TUTT low and associated trough are forecast to move further
westward through Wednesday. The precipitable water content is
expected to remain at normal levels between 1.75-2.00 inches
through at least tomorrow. Favorable upper level conditions will
remain across the region due to the proximity of the upper level
low. Therefore, another round of showers and thunderstorms is
expected across the islands through at least Wednesday afternoon.
At the same time, a strong Saharan Air Layer will filter quickly
from the east and a mid-to -upper level ridge will build over the
eastern Caribbean. This will bring hazy skies and an increase in
winds, particularly on Thursday. Shower activity will be limited
to local effects.


.LONG TERM...Friday through Wednesday...From Prev Disc...

Strong surface high pressure will remain the dominant feature across
the Atlantic and north of the region. This will maintain moderate
east to northeast winds Friday into Saturday while a tropical wave
will enter the eastern Caribbean and cross the forecast area. This
is expected to bring increasing moisture and instability to the
region along with a wind surge and moderate to strong southeasterly
winds by Saturday afternoon and on Sunday, as the tropical wave
exits the region. Accompanying and trailing the wave is an
extensive plume of dense Saharan dust which will quickly spread
across the region the rest of the weekend through Monday before
diminishing from Tuesday onwards. Winds are then to become more
easterly while another Tutt and induced surface trough approaches
from the east. Hot,humid and hazy conditions will likely persist
through the weekend.

Model guidance continued to initialize fairly well so far and still
suggests the most impactful period to be Friday through Saturday due
to increasing moisture convergence and instability with enhanced
overnight and afternoon convection expected due to the tropical wave
and cooler advective temperatures aloft. This will be followed by
hazy conditions as mentioned and a drier airmass due to the dense
layer of Saharan dust particulates which will maintain unseasonably
hot and humid conditions. Local temperatures are expected to continue
above normal with maximum daytime heat indices forecast to be elevated
to significant at times especially along the coastal and urban areas.
Marine conditions area also forecast to deteriorate Friday and into
the weekend due to the tightening of the local pressure gradient
and a wind surge which will increase the trade winds. Precautionary
statements and small craft advisories may be required for all or
portions of the local waters and passages through Saturday.

Sunday through Monday are expected to improve with typical summer
time weather and hot and hazy conditions. So far only isolated to
scattered locally and diurnally afternoon convection expected mainly
over the west and northwest sections of Puerto Rico. By late Monday
through the rest of the period, the upper ridge will erode as a Tutt
low is forecast to retrograde across the region and low level
moisture gradually increases. This in turn will increase the chance
for more frequent overnight passing showers and afternoon convection
across parts of the islands.

Otherwise based on the tropical weather outlook for the National
Hurricane center... Tropical cyclone formation is not expected
during the next seven days.


&&

.AVIATION...

(18z TAFs)

SHRA/TSRA cont ovr nrn PR and the lcl waters E of PR with some heavy
SHRA expected in the W and WNW portions of PR and downstream from El
Yunque or Vieques. Sct MVFR/IFR to result, altho TAF sites may see
these conds only briefly if at all. Winds 10-15 kt from the ESE with
gusts to 23 kt in sea breeze variations. Winds bcmg ESE-SE less than
10 kt aft 16/22Z in land breezes, but mstr will cont to incrs--
mainly over ern PR and the USVI. Sea breezes return in ESE-SE flow
at 12-18 kt with gusts to 26kt. Increasing Saharan dust aft 17/18Z.


&&

.MARINE...

A surface high pressure centered across the west central Atlantic and
an upper trough and associated induced low level trough crossing the
region will maintain a light to moderate east to southeast wind flow
with occasional showers and thunderstorms across the local waters
and passages. Winds will become more southeasterly and increase
to moderate to locally fresh by Wednesday. As the wind increases,
choppy seas will be likely across the local waters and passages,
resulting in seas up to 7 feet and winds up to 20 knots. Small
craft advisories and precautionary statement will be required by
then.


&&

.BEACH FORECAST...

For the remainder of the week, there will be a moderate risk of
rip current for most beaches and therefore life-threatening rip
currents will be possible in the surf zone.


&&

.SJU WATCHES/WARNINGS/ADVISORIES...

PR...None.

VI...None.

AM...None.
&&

$$

SHORT TERM, MARINE, BEACH...DSR
LONG TERM...RAM
AVIATION...WS