Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 191510
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1110 AM AST Wed Feb 19 2020

.UPDATE...Trade wind showers will continue to prevail across
the forecast area throughout the day today with some locally
induced afternoon showers over western Puerto Rico. Breezy. Some
changes were introduced to the forecast package to match current
weather conditions.

&&

.AVIATION...Mainly VFR conds to continue with -SHRA/VCSH
possible in and around the Leeward and USVI terminals as well
as JSJ. Aft 18/17z SHRA ovr JMZ will bring some periods of brief
MVFR conds through 18/22z. Winds 15-20 kts with some higher gusts.

&&

.MARINE...Hazardous marine conditions will continue to prevail
across the local waters with seas 6 to 8 feet and winds 15-20
knots. SCAs remain in effect.

&&

.PREV DISCUSSION... /issued 453 AM AST Wed Feb 19 2020/

SYNOPSIS...High pressure northeast of the area will bring breezy
conditions today and Thursday with fast moving showers that will
visit the northeastern two thirds of Puerto Rico. Some drying will
occur on Friday, then an approaching front will bring a modest
increase in the moisture to the area.

SHORT TERM...Today through Friday...

Little change is expected in the short-term forecast from yesterday.
The overall weather pattern continues to be unfavorable for
thunderstorms or intense rain showers. A trough is digging down to
our east at upper levels, with a ridge to our west providing warming
aloft. These warmer temperatures will suppress cloud development and
result in only shallow rain showers. At the surface, high pressure
to our north continues to drive breezy winds that will keep the
showers moving along and lessen their impact.

For today, isolated to scattered showers will continue this morning,
then increase in the afternoon as another patch of moisture moves
into the region and interacts with the sea breeze. Showers are most
likely over the higher terrain in Puerto Rico, and into the Atlantic
waters. The chance for flooding is very low, though ponding of water
on roadways is possible from passing showers. Showers will continue
into the nighttime, but drier air is expected to move in for
tomorrow. In fact, Saharan dust will make an appearance beginning
tomorrow, and though it won`t be a substantial dust event, there
will be a noticeable decline in visibilities. The dust is expected
to last into the weekend. This drier air and dust will reduce shower
chances, making later Thursday and all of Friday fairly uneventful
weatherwise.

LONG TERM...Saturday through Wednesday...
The ridge that dominated the area during the week at upper levels will
move east of the area Saturday and a long wave trough will sink
south into the Atlantic waters north of the area Sunday. By
Monday it will pass to the east.

A cold front will begin to approach the local area on Saturday. A
pre-frontal trough will also develop in the western tropical
Atlantic with the aid of a trough moving toward the area. The weak
trough at 700 mb will push into the area Sunday and Monday while
the front approaches the northwest corner of the forecast area.
Current models have considerably drier air trapped between the
pre-frontal trough and the front and greatly reduce the amount of
rain expected in the area due to the front, since a jet of air
from the southeast at lower levels will tend to push back at the
front and hold it just north of the area. By Wednesday, however,
the moisture from the two features merge over the area and
northeasterly flow at lower levels carries the day and allows the
front to pass with considerably drier air behind it. Nevertheless
would expect at least scattered to numerous showers in the area
Tuesday and Wednesday due to the convergence of these systems.
But, because relative humidities are generally less than 30
percent above 12 kft for the entire period rainfall amounts will
be modest and generally less than one inch on the most favored
slopes.

AVIATION...VFR conditions will continue for the most part at
all terminals. However, passing SHRA could produce brief MVFR
conditions. Winds this morning will be from the east at around 10
kts, and between 10-20 kts by this afternoon with higher gusts,
particularly associated with the showers. Though all terminals have a
chance for showers this afternoon, the driest location is likely
TJPS, with the best chance for showers at TJMZ/TJSJ. Maximum winds
55-70 kt btwn FL290-480. Winds nr FL290 will be nearly north, but
will back around to WNW by FL400.

MARINE...Surface winds up to 25 knots will drive seas up to 8
feet today. Winds and seas will gradually diminish, but some outer
waters will continue to see 7 feet or better on Friday. While all
areas should have seas below 7 feet by Friday afternoon, a better
set of north northwest swell is expected to raise seas to 7 to 8
feet beginning Sunday.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  85  74  85  74 /  50  50  50  50
STT  78  74  85  74 /  50  50  30  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk until 6 PM AST this evening for Culebra-
     Northeast-Southeast.

     High Rip Current Risk through late tonight for San Juan and
     Vicinity.

     High Rip Current Risk through Thursday afternoon for North
     Central-Northwest.

VI...High Rip Current Risk through Thursday afternoon for St Croix.

AM...Small Craft Advisory until 8 PM AST Thursday for Anegada Passage
     Southward to 17N-Caribbean Waters of Puerto Rico from 10 NM
     to 17N-Coastal Waters of Northern Puerto Rico out 10 NM-
     Mona Passage Southward to 17N.

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

     Small Craft Advisory until 2 AM AST Friday 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 until 8 PM AST this evening for Coastal
     Waters OF Northwestern Puerto Rico out 10 NM.

&&

$$

UPDATE...OM
AVIATION....OM
PUBLIC DESK...LIS



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