Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 200913

Area Forecast Discussion
National Weather Service San Juan PR
513 AM AST Fri Sep 20 2019

.SYNOPSIS...Hazardous marine conditions are expected to hold
through the weekend due to a series of northerly swells affecting
the local waters. As a result, a High Rip Current Risk, as well as
Small Craft, High Surf and Coastal Flooding Advisories remain in
effect. A wetter weather pattern is expected through most of the
forecast period. This will be the result of Hurricane Jerry`s
outer bands today through Sunday, followed by the arrival of a
potent tropical wave or potential tropical cyclone late Monday
night through the end of the workweek.


.SHORT TERM...Today through Sunday...

Showers and isolated thunderstorms resulting from an upper trough
west of the local area affected the western waters of our forecast
area, but it has been gradually improving as the night progressed.
This upper trough is expected to continue moving west today and an
upper high pressure will move in over the local area. That said, the
latest high resolution guidance suggests that showers and
thunderstorms will develop across NW-PR this afternoon, but some
forecast models also indicate some activity across eastern PR,
likely due to the decrease in wind speed causing convection much
further east than normal. Hurricane Jerry is expected to pass at
around 200 miles or more north northeast of the local islands late
tonight and Saturday, but the local winds will diminish greatly this
afternoon into Saturday. With that, there is a possibility of an
outer band to move in late tonight into early Saturday, which could
cause showers and thunderstorms across the local islands, including
the USVI.

The local wind flow on Saturday will become southerly as the day
progresses, even though is expected to be on the lighter side. This
southerly wind flow will combine with the available moisture and
local effects to cause the development of showers and thunderstorms
across central to northern Puerto Rico on Saturday afternoon. Then on
Sunday, another band of moisture could move in the morning, bringing
some shower activity. Then drier air expected to move in on Sunday
afternoon, but the local effects could play a role in developing
some shower and thunderstorms across northwestern PR.

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

Model guidance continues to suggest that a wetter pattern will
dominate the region through most of the workweek. But first, a
decrease in shower and thunderstorm activity due to a drop in
moisture content and the entrance of suspended Saharan dust in
the wake of Hurricane Jerry is expected on Monday. Nevertheless,
locally induced showers and possible isolated thunderstorms can be
expected in the afternoon.

The next moisture and instability enhancer, a potent tropical
wave, is expected to approach the region late Monday night into
Tuesday. As of 2 AM AST, this wave was located about 700 miles
east of the Windward Islands, and some development is possible
while it approaches and moves across the Windward Islands during
the weekend. As a result, the National Hurricane Center gives
this system a 30% chance of developing into a tropical cyclone in
5 days. Regardless of its development, model guidance suggests
that the bulk of this system will affect the region Tuesday and
Wednesday, while its trailing edge is expected to move across the
area on Thursday through at least Friday.


.AVIATION...VCSH expected across the local terminals today, but the
activity will be brief and is not expected to have a significant
impact on the local terminals. However, SHRA/TSRA development after
20/16Z expected across NW-PR that is expected to cause at least VCTS
at TJMZ and TJBQ, but it is possible also at TJSJ. Winds will be
from the E-ENE through the day with sea breeze variations after
20/13Z, but winds will become much lighter and variable at times
after 20/22Z. SHRA/TSRA activity could affect the local area once
again after 20/22Z, but this time possibly affecting the USVI.


.MARINE...A series of northerly swells, generated by Post-Tropical
Cyclone Humberto and Hurricane Jerry, will affect through the
upcoming weekend, maintaining hazardous marine conditions. As a
result, Small Craft Advisories are in effect for all but Caribbean
waters due to seas peaking between 7 and 10 feet today. By
tonight, seas are expected to increase up to 14 feet across the
outer Atlantic waters. Winds will range between 5 to 15 knots, but
variable as Hurricane Jerry moves north of the forecast area.

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.


SJU  92  77  91  78 /  40  40  60  60
STT  91  82  88  82 /  40  30  30  50


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

     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-

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



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