Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 240151

Area Forecast Discussion
National Weather Service San Juan PR
951 PM AST Thu Feb 23 2017

.UPDATE...The inherited weather forecast was not adjusted since
the latest guidance and observations were in agreement with the
inherited forecast.

Some showers affected the USVI today, leaving about a quarter of
an inch of rain in Saint Thomas and Saint John, while Saint Croix
received little to no rain. Portions of eastern, southern and NW-
PR received some rain but most of the amounts were minimal while
some areas received about a quarter of an inch of rain or slightly
over that, like it was the case for the San Juan metro area.

The winds are expected to remain from the south to southeast
through tonight with moisture decreasing slightly and gradually
until Friday. Therefore only isolated showers and mainly fair
weather is expected overnight. The drier air is expected to reach
the local area by Friday so only a slight chance of showers are
forecast for Friday.

The biggest changes to the forecast were on the marine and surf
zone conditions, more on that in the Marine section of the


.AVIATION...Mostly VFR conds expected at all TAF sites with brief
MVFR conds possible in and around TNCM/TKPK due to and area of
moisture moving thru til arnd 24/16z. Light passing showers still
possible at all taf sites except TJMZ/TJBQ till aft 24/14z SE winds
will continue 5-10 knots will but becoming light and variable
overnight and return aft 24/14z with sea breeze variations. mtn
obscurations likely until 24/16z then isold aftwds.


.MARINE...Some changes were made to the marine forecast given the
latest observations and guidance. A comparison between the model
guidance and the observations revealed that the models were
underestimating the wave heights, so we bumped up the wave heights
a little in our forecast for the next 48 hours as the northerly
swell invades the local waters. It is still expected for the swell
to peak locally on Friday but the seas may reach small craft
advisory criteria a bit sooner than expected according to the
latest observations. Buoy 41053 is already at 6.6 feet while the
models were estimating about 5 feet, so we made the adjustments
and we updated the small craft advisories for the different marine
zones. There were also changes in the surf zone forecast and the
high risk of rip currents were extended to the beaches of NW
Puerto Rico.


.PREV DISCUSSION... /issued 207 PM AST Thu Feb 23 2017/

A mid-upper level ridge is forecast to build from the west over
the local region through the end of the work week. An upper level
trough could weaken this ridge as it swing across the Western
Atlantic during the weekend. At the surface, a low pressure and
associated frontal boundary, near Eastern U.S., will continue to
push a surface high pressure into the Central Atlantic. This
overall surface pattern will cause the local winds to become from
the south during the weekend.

A surge of tropical moisture moved over the region today. This
surface advection produced passing showers across the
municipalities of Eastern Puerto Rico and the U.S. Virgin Islands.
Although a southerly wind flow prevailed across the region, the
cloudiness damped the local maximum temperatures this afternoon.
For the rest of the afternoon hours, afternoon convection is
expected along and to the north of the Cordillera Central,
including San Juan Metro Area and Northwest Puerto Rico. Under
the southerly wind flow quick passing showers cannot be ruled out
across the southern sections of Puerto Rico and downwind from the
U.S. Virgin Islands.

A seasonable weather pattern will continue to prevail across the
local islands through early next week under a mid level ridge and
near normal precipitable water. A southeasterly wind flow will
continue through the weekend as a surface low and associated front
move across the Western Atlantic ocean and a surface high north
of the area shifts further east.

Mostly VFR conds expected at all TAF sites with brief
MVFR conds possible in and around JMZ/JBQ due to SHRA development
through 22z. Light passing showers still possible at IST/NCM as well
as JSJ through at least mid afternoon. SE winds will continue 10-15
knots with some sea breeze variations but becoming light and
variable overnight.

Seas are expected to increase across the Atlantic Waters,
therefore a small craft advisory is in effect for the Offshore
waters through at least Saturday. Mariners can expect seas up to 5
ft increasing at around 6 ft across the Atlantic Nearshore water
and Caribbean passages tonight. Beach goers should exercise
caution from the Northwest to Northeast coastline of Puerto Rico,
Culebra and Northern U.S. Virgin Islands due to a high risk of rip
current late this afternoon through at least tomorrow.


SJU  74  87  74  87 /  20  20  10  20
STT  74  83  75  83 /  20  20  20  20


PR...High Rip Current Risk through Friday afternoon for Culebra-
     Mayaguez and Vicinity-North Central-Northeast-Northwest-San
     Juan and Vicinity-Southeast-Western Interior.

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

     Small Craft Advisory from 8 AM to 8 PM AST Friday for
     St.Thomas...St. John.. and Adjacent Islands.

AM...High Rip Current Risk through Friday afternoon for Coastal
     Waters of Northern USVI and Culebra out 10 NM-Coastal
     Waters of Southern USVI Vieques and Eastern Puerto Rico out
     10 NM.

     Small Craft Advisory from 8 AM to 8 PM AST Friday for Anegada
     Passage Southward to 17N-Coastal Waters of Northern USVI
     and Culebra out 10 NM.

     Small Craft Advisory from 8 AM Friday to 2 AM AST Saturday for
     Coastal Waters OF Northwestern Puerto Rico out 10 NM-
     Coastal Waters of Northern Puerto Rico out 10 NM-Mona
     Passage Southward to 17N.

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



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