Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service San Juan PR
302 PM AST Thursday Apr 17 2014

Synopsis...upper level ridge will hold through the end of the week.
Ridge will flatten early next week as southern stream perturbations
stream north of the area. Strong winds and rough seas expected Thursday
through Sat.


Discussion...windy and wet tonight in windward and higher elevs.
Drying indicated through the day Friday and this seems reasonable
per latest blended tpw product which shows dryer air upstream
northeast of the leewards and under upper level ridge axis.

Models continue to indicate middle-upper level ridge axis eroding by
Monday as inflow of southern stream energy moves into the area. This
results in moisture deepening as subsidence inversion erodes.
However...the models are not as aggressive as they were yesterday
with the depth of moisture and now indicate lesser rainfall accumulations.


Aviation...sct-bkn low level cloud will continue westward across the flying
area by the way the northern leewards and PR with embedded passing -shra/rain showers
and few towering cumulus. Expect brief passing showers to affect most taf sites
until at least 18/22z. Prd of MVFR in rain showers/low ceiling with surface wind gust
up to 26 kts will remain possible mainly with the passing showers. Brief
mountain top obscure will affect portions of the Central Mountain range until
17/22z. Low level winds mainly from east at 15-20 kts below fl150...becoming from
north-northwest and increase west/heat above to maximum wind of around 60 kts near fl400. From
18/03z-18/12z another surge of scattered-broken l/level clouds west/embedded
isolated-scattered rain showers is forecast to affect parts of eastern PR...tjsj...tisx and


Marine...east winds up to 22 knots and rough seas. Guidance
suggests seas up to 9 feet in Atlantic waters. Believe seas will be more like
in the 5-7 feet range but will keep 6-8 feet for continuity.


Preliminary point temps/pops...
sju 77 85 76 85 / 60 60 40 40
stt 77 85 77 86 / 50 50 40 40


Sju watches/warnings/advisories...

Coastal waters...Small Craft Advisory from 6 PM this evening to 6 am AST Sunday
for Anegada Passage southward to 17n-Mona Passage southward
to 17n.

Small Craft Advisory from midnight tonight to 6 am AST Sunday
for Caribbean waters of Puerto Rico from 10 nm to 17n-
coastal waters of northern Puerto Rico out 10 nm-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 2 PM AST Friday for coastal
waters of southern Puerto Rico out 10 nm.

Small Craft Advisory from 6 am Friday to 6 am AST Sunday for
coastal waters of northwestern Puerto Rico out 10 nm.

Small Craft Advisory until 6 am AST Sunday for Atlantic waters of
Puerto Rico and USVI from 10nm to 19.5n.