Area Forecast Discussion
Issued by NWS San Juan, PR

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299
FXCA62 TJSJ 281744
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
144 PM AST SUN AUG 28 2016

.SYNOPSIS...Tutt low now centered just north of the northern
Leeward Islands will continue to slowly shift westward across the
region overnight through Monday. This pattern should briefly place
most of the forecast area on the subsident side of the upper trough
which will should be somewhat of a limiting factor for significant
convective development. However, the broad trough across the western
caribbean which extends into the southwest Atlantic will maintain
a sufficiently moist environment across the region today. Satellite
imagery showed mid to upper level cloud debris from convection around
the tutt low being transported southwards across the forecast area.

&&

.DISCUSSION...Although occasional transport of mid to upper level cloudiness
across the region is expected today ..still expect sufficient low level
moisture convergence and instability across the region to allow for
afternoon convection across parts of the islands. Over Puerto Rico.
because of the light wind flow, now expect most of the convection to
be focused across the interior and west to southwest sections of the
island. Over the U.S Virgin Islands any showers that do develop should
occur mainly on the windward side of the island steered by the prevailing
east southeast wind flow. Afternoon showers and thunderstorm activity
may produce locally heavy rainfall at times and could lead to minor
ponding of water on roadways and in poor drainage areas. Expect
the convection over land to diminish around sunset, leaving variably
cloudy to partly cloudy skies over land areas.

During the overnight and early Monday morning, showers and thunderstorms
are expected redevelop over the coastal waters surrounding the islands,
as the upper low and induced surface trough will enhance shower development
as it moves westward. Therefore showers may affect portions of the north
and east coastal areas and produce periods of moderate to locally heavy
rainfall. During the afternoon on Monday ...expect the tutt low to then
be in a position to favorable upper level instability and better chance
of enhanced afternoon convection across the northern half of Puerto
Rico.

A somewhat drier weather pattern is so far expected on Tuesday
and into the latter part of this upcoming week, as high pressure
will build aloft and to the north of the region with lesser tropical
moisture advection. However...sufficient moisture will be available
each day to allow for the typical passing early morning showers followed
by isolated to scattered shower activity across parts of the interior
and west sections of Puerto Rico with lesser activity expected for the
U.S Virgin Islands.

&&

.AVIATION...Showers and thunderstorms are possible for the southern
half of Puerto Rico and all USVI terminals until 28/22Z. Isolated
tstms will affect the vicinity of TJSJ...TJBQ and TIST after 29/04Z
and through 29/12z with mountain top obscuration across the
Cordillera Central of PR. Low level winds will be mainly east at 10
knots overnight increasing to 10 to 15 knots after 29/13Z.

&&

.MARINE...Tranquil marine weather conditions are expected to continue
through at least Tuesday. However, isolated thunderstorms with areas
of locally heavy rainfall and dangerous lightning will remain possible
across the regional waters as the TUTT Low moves across the region
overnight through Monday.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  78  91  80  92 /  20  30  10  10
STT  80  87  81  88 /  40  40  10  20

&&

.SJU Watches/Warnings/Advisories...
PR...None.
VI...None.
AM...None.
&&

$$

11/09



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