Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Juan PR
412 am AST Friday Oct 31 2014
Synopsis...upper level ridge will build through the weekend. Deep
cutoff low expected to evolve over the Windward Passage/central
Caribbean middle next week and bring cooler and unsettled weather.
Discussion...deep convection over the USVI and adjancent waters
is being enhanced by an upper level trough currently moving
through the area with clearing ongoing over western PR. Trough axis will
pull away from the area today with heights aloft rising rapidly
leading to improving weather conditions. Some afternoon convection
still possible over northern PR this afternoon but areal coverage and
intensity will be significantly less than yesterday afternoon and
evening. Heights aloft continue to rise through the weekend with
further drying expected.
On Monday...heights aloft will fall sharply as an upper level
trough cuts off over the SW Atlantic. 31/00z European model (ecmwf) more aggressive than
GFS showing an anomalous deep cutoff over the central Caribbean.
Combination of height falls and strengthening trade winds will
lead to rapid moisture advection Monday night through Tuesday evening
with showers increasing in areal coverage over eastern PR during the
night/early morning and western PR during the afternoon. Substantial
middle-high level cloud deck associated with an upper level jet
streak with cooler temperatures/lower heights is forecast by global models
next week should bring a sig relief to the hot weather of this weekend.
Upper level low begins to fill on Wednesday with weather conditions improving
somewhat although considerable middle-high level clouds are likely to
persist for several more days.
Aviation...shra/tsra around the USVI will cause tempo MVFR conds
with at tisx and tist until 31/12z...with ceilings around fl020-040 and
reduction in visibility to around 3 miles as the activity affects
the terminals...otherwise vcsh/thunderstorms in the vicinity is likely. Thunderstorms in the vicinity is also possible
for tncm. The rest of the terminals should remain VFR through the
forecast period. Afternoon convection expected across northwest-PR which
may briefly affect tjbq between 31/18z and 31/22z.
Marine...south or south-southeast winds 10 knots or less through Sat. Trades
return Sat night and strengthen up to 20 knots. Seas mainly 2-3 feet
through sun then build 5-7 feet by Monday night in north-northwest swells and east-northeast
wind waves. This likely to result in rough surf conditions with
high risk of rip currents on Atlantic and northwest PR beaches.
Preliminary point temps/pops...
sju 89 80 88 81 / 50 0 10 10
stt 89 82 89 82 / 20 10 10 10