Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Juan PR
453 am AST Sat Mar 28 2015
Synopsis...broad middle to upper level ridge will continue as the main
weather feature across the region through Sunday. By Sunday night
and into Monday the middle to upper ridge will erode in response to a
deep/amplifying long wave trough moving across the western Atlantic.
Discussion...Doppler weather radar detected only few isolated
passing showers over the surrounding waters overnight and early this
morning...but no precipitation was detected over land areas as the
northeast Caribbean remains under the influence of a middle to upper
level ridge. This feature is expected to remains as the main weather
feature today and early Sunday...providing subsidence inversion over
the region. Thus...limited shower activity is expected for the rest
of the weekend with only the typical trade wind showers over the
U.S. Virgin Islands and eastern Puerto Rico overnight and early in
the mornings with some convection across western and interior
sections of Puerto Rico each afternoon. By late Sunday into the
early part of next week...latest GFS model guidance model continued
to suggest the dissipating frontal boundary/shear line to stall just
north of the region. Expect some low level moisture transport and
convergence across the forecast area to increase the chances for
shower development across the coastal waters and parts of the
islands. In addition...the erosion of the upper level ridge by late
Sunday and Monday...will also slightly increase the potential for
isolated thunderstorms in response to weakening cap inversion.
Some drying expected Wednesday night into Thursday.
Aviation...VFR conds expected at all taf sites through the forecast
period. Chance of brief MVFR conds in ceiling/rain showers from 28/18z to 28/22z in
and around tjbq/tjmz. Surface winds until 28/12z east less than 10 kts...
after 28/14z...mainly from east at 10-15 knots gusting to near 25 kts with
local sea breeze variations. L/level winds east-southeast up to 25 knots below
fl100...becoming from north and decr west/heat up to fl250...then from northwest and increase
west/h to maximum wind around 45 kts near fl400.No sig operational weather impacts
at this time.
winds up to 20 knots and seas up to 6 feet are expected across
the regional waters. However ocassionally seas will reach up to 8
feet for short periods of time. Small craft are urged to exercise
caution across most of the local waters.
Preliminary point temps/pops...
sju 89 74 88 75 / 0 10 10 10
stt 86 75 85 74 / 10 10 10 10