Area Forecast Discussion
Issued by NWS San Juan, PR

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437
FXCA62 TJSJ 201737
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
137 PM AST Fri Sep 20 2019

.SYNOPSIS...

As hurricane Jerry passes to our north, a few impacts will be felt
across the region. These include rough marine conditions and
showers associated with the outer bands of the storm. These
effects will be felt into Sunday, after which a brief period of
drier air and Saharan dust moves in. Our attention will then turn
to a vigorous tropical wave which the National Hurricane Center is
calling Invest 99L. See the long term discussion for the
potential impacts of this system.

&&

.SHORT TERM...Rest of today through Sunday...

A mid to upper level high pressure ridge will continue to move in
over the local area today through the weekend. Recent high
resolution model guidance along with the overall weather pattern
continues to suggest the potential for showers and isolated
thunderstorms developing mainly across NW PR this afternoon.
Forecast models also suggest some shower activity possible over
eastern PR, but mainly in the form of isolated streamers of short
duration.

Based on the latest guidance from the National Hurricane center in
Miami...Hurricane Jerry is expected to pass well north northeast of
the local islands late tonight through Saturday. The local wind flow
will diminish significantly beginning this afternoon and through the
weekend.  However, it is quite possible that the outer feeder bands
generated from Hurricane Jerry will continue to propagate west and
south of the center and occasionally affect all or portions of the
islands from time to time...becoming more frequent overnight through
early Saturday. These bands may bring sudden bursts of convection
with showers and thunderstorms and higher wind gusts. There is also
a slight possibly a few isolated gusts producing winds near tropical
force winds over portions of the forecast area particularly
around the northern USVI and portions of Northern and eastern PR.
This is however based on the latest Hurricane track and intensity
and is subject to change.

The local wind flow on Saturday will become more southerly as the
day progresses, although they will be fairly light under the
influence of Hurricane Jerry. This southerly flow will combine with
the available moisture and local effects to cause the development of
showers and thunderstorms across portions of south and east coastal
areas during the morning hours followed by central to northern
Puerto Rico on Saturday afternoon. Then on Sunday, another surge of
of moisture will move across the area during the morning hours,
bringing brief shower activity.

A somewhat drier air mass is expected to move in by Sunday
afternoon. However, local effects, daytime heating and available low
level moisture convergence will still favor afternoon showers and
isolated thunderstorm development mainly over parts of central
and northwestern PR.


.LONG TERM...Monday through Friday...

After the rainbands associated with Hurricane Jerry move out, drier
conditions are forecasted. A Saharan air layer with associated dust
will filter in on Sunday and peak in concentration for Monday.
However, forecast models have backed off a bit on the strength of
the dust event, though hazy conditions are still likely. Despite the
drier air, isolated showers are still possible.

Thereafter, our weather gets more interesting as a vigorous
tropical wave moves up from the south for Monday night and into
Wednesday. Currently this tropical wave is located 700 miles east
of the Windward Islands, and will move into the Caribbean Sea
this weekend. The National Hurricane Center gives the wave a 30%
chance of development in the next 5 days. Long-range models
currently expect the system to bring a lot of precipitation our
direction for especially next Tuesday, where the GFS is predicting
almost 2.5 inches of precipitable water. Furthermore, due to the
projected slow movement of the storm through our region, the
possibility exists for a very wet middle of the next week with a
threat for urban and small stream flooding. Forecast models
diverge substantially after mid-week, though there does appear to
be ample moisture to drive scattered showers through the end of
the week.


&&

.AVIATION...VCSH/Isold TSRA fcst across the most local terminals
today, with ocnl feeder bands from Hurricane Jerry affecting parts
of the northern Leewards durg the prd. This may bring brief MVFR
conds and gusty winds. This activity will later spread into the
local flying area aft 21/23Z and affect local terminals from time to
time but prevailing VFR is fcst. SHRA/Isold TSRA development fm
20/17Z-20/22Z across NW PR with psbl VCSH/VCTS at TJMZ/TJBQ...
steered by the prevailing SE wind flow.  SFC winds fm E-ENE w/sea
breeze variations and ocnly hir gusts...bcmg LGT/VRB aft 20/22Z.


&&

.MARINE...

We continue to be impacted by swells from Post-Tropical Cyclone
Huberto, as well as a rapidly weakening Hurricane Jerry. Buoy 41043
in the Atlantic waters has measured waves of 7-9 ft throughout the
day, and seas are expected to increase as Jerry passes to the NE.
The good news with Jerry is that it has weakened substantially this
morning, and will be a weak hurricane or strong tropical storm, of
fairly small size as it moves north. Therefore, we are still
forecasting waves above 10 feet for the Atlantic, but not as much as
was expected. Winds will range between 5 to 15 knots, but variable
as Hurricane Jerry passes by.

The long period swell will cause breaking waves of 10 to 15 feet and
life threatening rip currents for the beaches along the western, and
northern coast of Puerto Rico, northern Vieques, Culebra, St.Thomas
and eastern St. Croix through Sunday. In addition, coastal flooding
will be possible along the coastal sections of northern Puerto Rico
through this evening.

Please refer to the latest Coastal Hazard Message (CFWSJU) and
Marine Weather Message (MWWSJU) for the latest information.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  77  91  78  92 /  30  60  60  60
STT  82  88  82  89 /  50  40  50  50

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Sunday afternoon for Culebra-
     Mayaguez and Vicinity-North Central-Northeast-Northwest-San
     Juan and Vicinity-Southeast.

     High Surf Advisory until 6 AM AST Sunday for Culebra-Mayaguez
     and Vicinity-North Central-Northeast-Northwest-San Juan and
     Vicinity-Southeast-Southwest.

     Coastal Flood Advisory until 6 PM AST this evening for North
     Central-Northeast-Northwest-San Juan and Vicinity-Southeast.

     High Rip Current Risk through Saturday afternoon for Southwest-
     Vieques.

VI...High Rip Current Risk through Sunday afternoon for
     St.Thomas...St. John...and Adjacent Islands.

     High Surf Advisory until 6 AM AST Sunday for St.Thomas...St.
     John...and Adjacent Islands.

     High Rip Current Risk through Saturday afternoon for St Croix.

AM...Small Craft Advisory until 2 AM AST Sunday for Coastal Waters of
     Northern Puerto Rico out 10 NM-Coastal Waters of Northern
     USVI and Culebra out 10 NM-Mona Passage Southward to 17N.

     Small Craft Advisory until 8 PM AST Sunday for Atlantic Waters
     of Puerto Rico and USVI from 10 NM to 19.5N.

     Small Craft Advisory until 8 AM AST Saturday for Coastal Waters
     of Southern USVI Vieques and Eastern Puerto Rico out 10 NM.

     Small Craft Advisory until 8 PM AST Saturday for Anegada Passage
     Southward to 17N-Coastal Waters OF Northwestern Puerto Rico
     out 10 NM-Coastal Waters OF Southwestern Puerto Rico out 10
     NM.

&&

$$

SHORT TERM...RAM
LONG TERM....MB



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