Advisory NPW Special Advisory — Sun Jul 28, 2024 5:21 AM

NPWSJU) was
issued across these areas, and could likely be issued once again on
Monday and Tuesday. For the rest of today, an advective weather
pattern should prevail across the local waters with passing showers
moving over the islands through the morning hours, then afternoon
showers with isolated thunderstorms should develop mainly over the
interior and western sections of PR.

On Monday, a TUTT induced perturbation is expected to move from the
east and bring an increase in moisture content. Precipitable water
content is expected to increase between 1.75-2.00 inches by Monday
afternoon. Therefore, showers will increase in coverage as well as
the potential for better organized afternoon convection over
portions of the eastern interior, central, and western Puerto Rico.
Urban and small stream flooding can be expected with this activity.
Drier conditions and hazy skies are expected on Tuesday as a weak
Saharan Air Layer filters from the east. Regardless, showers could
develop over western PR during the afternoon due to diurnal and
local effects.

.LONG TERM...Wednesday through Sunday

The National Hurricane Center now puts the tropical wave at a 40%
chance of developing into a tropical cyclone in the next seven days.
However, the global models that do develop it have solutions that do
so after passing Puerto Rico. ECMWF ensemble members (EPS) show most
development occurring north or northwest of Puerto Rico, while the
CMC develops it over the Caribbean waters, well southwest of the
forecast area. A much lower percentage of GFS ensemble members
(GEFS) have the tropical wave developing at all, but those solutions
usually appear after passing the forecast area. Additionally, the
broad moisture field from this wave seems to protect it from much
Saharan dust intrusion. Therefore, the limiting factor of the
Saharan Air Layer may not be the case with this tropical wave.

Regardless of development, we can expect a very wet and unstable
weather pattern by mid-week of next week through at least Friday.
Well above normal moisture content will engulf the forecast area
with prolonged periods of precipitable water values close to the
99th percentile or maximum for this time of year. Several features
indicate favorable conditions aloft, such as a drop in 250 MB
heights, cooler 500 MB temperatures, and steeper low- to mid-level
lapse rates. The combination of instability with plenty of
tropical moisture will enhance deep convective activity. Both the
ECMWF and GFS Galvez- Davison Index indicate the potential for
scattered thunderstorms capable of producing heavy rainfall.

The QPF ECMWF Extreme Forecast Index also indicates that most of its
ensemble members predict the potential for a well above normal event
compared to the model climatology. However, it locates most QPF
north of Puerto Rico. So far, confidence is low as it is still
uncertain how much it can intensify before it reaches the northern
Caribbean and the exact path that this wave will take, which will
ultimately dictate its potential impacts on our region. Therefore,
continue to monitor the forecast, but be mindful that weather
conditions will shift to a more unstable and wet pattern at the
beginning of the long-term forecast.

The rest of the long-term forecast will depend on the lingering
effects of this tropical wave. Model guidance suggests the
persistence of instability aloft as some troughiness remains over
the forecast area. Therefore, expect active afternoons, particularly
over the Cordillera Central and western Puerto Rico, with developing
streamers downwind of the USVI and mountainous areas such as El
Yunque. This convective activity will be driven by an easterly
steering wind flow. For this reason, the flood risk will remain
elevated throughout the long-term forecast.


&&

.AVIATION...
(06Z TAFS)

Mainly VFR conditions are expected to prevail across all terminals
during the next 24 hours. However, trade wind SHRA could move at
times across the USVI and eastern PR terminals throughout the day.
This may cause brief MVFR cigs. Afternoon SHRA/TSRA is expected to
develop btw 28/18z-22z in the vcty of TJPS/TJBQ. East winds expected
at 12-16 kt with higher gusts and sea breeze variations aft 28/14z.


&&

.MARINE...

The pressure gradient over the local waters will tighten due to the
interaction of the surface high-pressure across the central Atlantic
and low-pressure building over Central America. This will support
moderate to fresh easterly winds and choppy seas in the next few
days. Trace of Saharan dust will result in slight hazy skies today,
with thunderstorms moving over western waters each afternoon. By
midweek, a vigorous tropical wave is forecast to promote an increase
in shower and thunderstorm activity across the regional waters along
with hazardous seas.

&&

.BEACH FORECAST...

Low rip current risk will prevail today for all the local beaches.
Increasing winds will promote moderate rip current risk throughout
the week.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon
     for PRZ001-003-005-007-008-010-011.

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

AM...None.
&&

$$