Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 190257 CCA
AFDSJU

Area Forecast Discussion...CORRECTED
National Weather Service San Juan PR
1057 PM AST Tue Feb 18 2020

.UPDATE...
No change to the inherited short term forecast package and reasoning
at this time. Recent GFS model guidance initialized fairly well
and continued to suggest occasional surges of trade wind moisture
during the overnight and early morning hours, carried by the
brisk easterly trades. Brief wind gusts between 25 to 30 mph
accompanied some of the passing showers as they moved across the
coastal waters and brushed portions of the islands from time to
time.

&&

.AVIATION...Prevailing VFR at all terminals but TEMPO MVFR psbl
AT TJSJ/TISX/TIST/TNCM/TKPK til at least 19/06Z due to SHRA/-SHRA
and low cig. Isold-Sct shra ovr regional waters btwn islands til
19/14Z. SCT ocnl BKN lyrs nr FL025...FL050...FL080 durg prd. Sfc
wnds fm E 10-15 kts with brief wnd gust mainly with passing SHRA.

&&

.MARINE...No change to previous marine discussion. Choppy and hazardous
seas will continue overnight and through the end of the work week.
Recent data from surrounding buoys continued to suggest moderate
to fresh easterlies of 15 to 20 knots with occasionally higher
gusts between 25 to 30 knots.

&&

.PREV DISCUSSION... /issued 509 PM AST Tue Feb 18 2020/

SYNOPSIS...A series of surface high pressures across the North
Atlantic will continue to result in brisk easterly trade winds
through at least Thursday. Patches of low-level moisture embedded
within the easterly trade wind flow will move across the area from
time to time to result in passing showers. However, given the
unfavorable conditions aloft, significant rainfall activity is not
expected.

SHORT TERM...Tonight through Thursday...

Overall, a fairly benign weather pattern is expected to prevail
across the area through the short-term period. Aloft, the region
will be located on the western side of a trough over the far western
tropical Atlantic and on the eastern side of a ridge building over
the western and central Caribbean. This will provide subsidence
aloft, limiting the development of significant showers.

At lower-levels, high pressure over the far northeast Atlantic and
another high pressure moving over the north-central Atlantic will
maintain the local pressure gradient tight. Therefore, brisk
easterly trade winds between 15 and 25 mph with higher gusts are
expected, especially from the mid-morning through the afternoon
hours. These easterly trade winds will also drive patches of low-
level moisture into the region from time to time, resulting in brief
light to moderate showers, especially across portions of eastern
Puerto Rico and the USVI. Some afternoon showers are possible across
western Puerto Rico due to local and diurnal effects. Given the
unfavorable conditions aloft and the fast low-level flow that will
keep these showers moving fast, only minor rainfall accumulations
are expected.

LONG TERM...Friday through Tuesday...

PREV DISCUSSION... /issued 529 AM AST Tue Feb 18 2020/

At mid and upper levels a vigorous trough with northeast-
southwest orientation across the western tropical Atlantic will
pull away on Friday leaving northwest flow over the area. On
Saturday a weak trough at upper levels will pass through the
area, then on Sunday a strong long wave trough will pass north of
the area over the Atlantic waters at both mid and upper levels.
As this trough at upper levels moves east, northwest flow will
resume.

At lower levels the passage of a weak trough on Friday and the
approach of a cold front from the northwest will cause low level
winds to become light and in places variable. Low moisture levels
on Friday will bring mostly sunny conditions with some above
normal temperatures over the islands. Low level moisture is patchy
and wind patterns are too light to predict over the weekend which
will lead to scattered showers of a local nature, generally over
higher terrain. During this period persistent showers in weak and
variable flow dominated by land and sea breezes could lead to
localized urban and small stream flooding. On Monday and Tuesday
moisture increases and the chance of showers improves, but very
moist conditions are localized and transitory, making shower
activity erratic. Winds at lower levels gradually become easterly
again, but remain light so interior Puerto Rico is the most likely
to see showers in sea breeze convergence with only scattered
showers elsewhere.

AVIATION...VFR conditions will continue with easterly winds at 10
to 20 kt with higher gusts, especially in and near the passing SHRA.
Passing SHRA will affect the terminals at times. JMZ/JPS will
observe afternoon SHRA through 18/23z. Similar weather pattern
will continue through the forecast period.

MARINE...The combination of a weak northerly swell and fresh
easterly trade winds of up to 20 kts will result in choppy and
hazardous seas of up to 7-8 feet across most of the regional
waters through at least Thursday. Therefore, small craft
advisories are in effect for most of the regional waters. There is
also a high risk of rip currents for the northern facing beaches
of Puerto Rico and Culebra as well as Cramer Park Beach in Saint
Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  74  84  74  84 /  50  30  50  30
STT  74  84  74  84 /  50  20  50  30

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Wednesday afternoon for Culebra-
     Northeast-San Juan and Vicinity-Southeast.

     High Rip Current Risk through late Wednesday night for North
     Central-Northwest.

VI...High Rip Current Risk through Wednesday 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-Mona Passage Southward to 17N.

     Small Craft Advisory until 8 PM AST Wednesday for Coastal Waters
     of Northwestern Puerto Rico out 10 NM-Coastal Waters of Northern
     Puerto Rico out 10 NM.

     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.

&&

$$

SHORT TERM...RAM
LONG TERM....GL
PUBLIC DESK...TW


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