Area Forecast Discussion
Issued by NWS San Juan, PR

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXCA62 TJSJ 201502
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1102 AM AST Mon Nov 20 2017

.UPDATE...

At this time no showers across Puerto Rico and the U.S. Virgin
Islands but conditions will gradually change. The local weather is
being influenced by a weak shear axis to the north and moist
southerly winds. In the Caribbean waters there is a weak surface
low that is firing scattered showers and thunderstorms to the
southwest of Puerto Rico. This feature is enhancing low level
moisture convergence across the area with a plume of moisture
moving to the northwest. This moisture will arrive across the
southwest, northwest, western interior, north central Puerto Rico
this afternoon and linger through the evening. The areas listed
above have received heavy rain over the last several days which
has caused saturated soils, and any additional rainfall could
cause urban and small stream flooding, and inundation of low-lying
and poorly drained areas.

Tuesday the trough of low pressure will begin to pull away from
the area and allow an upper level ridge of high pressure to nose
in over the region. This will give Puerto Rico and the U.S.
Virgin Islands a brief reprieve from the the heavy rainfall by
limiting the influx of deep tropical moisture.

&&


.AVIATION...

Aviation...SHRA/ and diminishing TSRA expected to continue across
the local area thru 20/02Z, causing VCSH/VCTS across the
terminals with TEMPO MVFR conds possible at TJBQ and TJMZ thru
20/02Z. VFR conds to continue thru 20/15Z with CIGS BLO FL120 and
mtn obscurations. Southerly winds sfc to FL200 gradly shifting to
SE 10 to 20 kt by 20/18Z. Maximum winds WSW 30 kt around FL400
thru 20/18Z.

&&

.MARINE...

Seas 3 to 5 feet are expected today across the local waters. Winds
10 to 15 kts from the southwest. There is a moderate risk of rip
currents today along the northeast, north and northwest coast of
mainland Puerto Rico and Culebra. Small sections in southwest
Puerto Rico also has a moderate risk of rip currents as well as
the northern and eastern beaches of Vieques, the north and
northwest beaches of Saint Tomas and Cramer Park in Saint Croix.

&&

.PREV DISCUSSION... /issued 430 AM AST Mon Nov 20 2017/

SYNOPSIS...A shearline just to the northwest of the local area is
now dissipating, but above normal moisture will remain over the
local area today. Winds will be southeasterly today but will turn
easterly as a surface high pressure moved over the western
Atlantic, north of the local islands. Showers and thunderstorms
are expected today, however, upper ridge will dominate the local
area starting on Tuesday, stabilizing the local atmosphere just
as drier air moves in, which will cause a decrease in shower and
thunderstorm activity, even after moisture increases slightly on
Wednesday since the upper ridge will remain for the next several
days.

SHORT TERM...Today through Wednesday...

Mostly cloudy skies prevailed across the forecast
area overnight and early this morning. Showers were observed
across the local waters but none over land areas. Coastal
temperatures were in the mid to upper 70s under light and variable
winds.

Lingering moisture associated with a dissipating shear line will
continue to prevail across the local isles today. Although latest
guidance continues to suggest precipitable water decreasing somewhat
across the area as well as less coverage of showers and
thunderstorms, there still a high chance for showers/thunderstorms
to form in the southeasterly flow off of El Yunque and into the San
Juan Metro Area and over the northwest quadrant of Puerto Rico. Due
to already saturated soils, any prolonged period of heavy rainfall
will result urban flooding and sharp rises along small streams and
rivers as well as mudslides in areas of steep terrain. Although a
mid to upper level ridge will build across the forecast area and
hold through the forecast period, easterly winds will continue to
bring patches of low level moisture to keep the chance of passing
showers Tuesday and Wednesday. Therefore, expect a seasonable
weather pattern with passing showers across USVI and E PR as well as
limited shower activity across west Puerto Rico both days.

LONG TERM...Thursday through Tuesday...

Late in the workweek into early next week, the available moisture
will be rather variable, with patches of moisture and patches of
drier air moving through the local area generally speaking. There
will be a day with near normal moisture then a day with lower
moisture followed by higher moisture. This pattern of somewhat
patchy moisture normally causes brief and isolated showers in
the morning and overnight hours with locally induced showers in
the afternoon but generally not very intense or widespread, which
will likely be the case late this week and at least into the
weekend since an upper high pressure is expected to prevail over
the local area. The expected equivalent potential temperature
indicates mostly stable conditions as well, therefore at this
time we expect some but not much weather late this week into
early next week.

AVIATION...Mostly VFR conds expected through 20/16z. SHRA/TSRA
expected in the afternoon to result in MVFR conds in and around
JSJ/JBQ and JMZ through 20/22z. Elsewhere VCSH expected. ESE winds
at around 10 knots with some sea breeze variations, becoming light
and variable overnight.

MARINE...Seas of 3 to 5 feet are expected today across the local
waters for the next few days. Winds will be up to 10 knots today
from the southeast, increasing to up to 15 knots from the east on
Tuesday and for the next several days after that. There is a
moderate risk of rip currents today along the northeast, north and
northwest coast of mainland Puerto Rico and Culebra. Small
sections in southwest Puerto Rico also has a moderate risk of rip
currents as well as the northern and eastern beaches of Vieques,
the north and northwest beaches of Saint Tomas and Cramer Park in
Saint Croix.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  86  76  90  76 /  50  20  20  20
STT  85  76  86  77 /  50  20  20  30

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Flash Flood Watch until 2 PM AST this afternoon for Northwest-
     Western Interior.

VI...None.
AM...None.
&&

$$

SHORT TERM...TW
LONG TERM....JA


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.