Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Juan PR
449 am AST Sat Sep 5 2015
Synopsis...middle to upper level ridge will continue to shift westward
from across the tropical Atlantic and displace the TUTT which will
move farther west of the region. Associated TUTT low will continue
to lift west northwest while weakening. A TUTT induced low level
trough with axis now crossing the eastern Caribbean will continue
westward across the forecast area during the rest of the day. No
significant amounts of moisture was noted accompanying this feature.
However...satellite imagery and Doppler weather radar both suggest
shallow moisture and convection moving across the regional waters
and brushing part of the coastal areas this morning.
Another tropical wave with axis near 57 west...will enter and
move across the eastern Caribbean later tonight through Sunday.
Fragments of moisture just ahead of and trailing the wave will
move westward across the regional waters later tonight through
Sunday. At this time...no significant deep moisture advection is
anticipated with this wave.
Discussion...fairly light easterly trades are to persist during
the next few days...as weak surface high pressure ridge will linger
north of the region. This is to support a loose local pressure gradient
resulting in increasing land and sea breeze convergence. The approaching
wave along with moisture convergence and diurnal effects will give way
to afternoon convection across parts of the central and west sections
of Puerto Rico during the afternoon hours. Passing showers will continue
to affects parts of eastern Puerto Rico as well as portions of the Virgin
Islands during the rest of the morning hours.
By Sunday...as the tropical wave moves across the region expect
another quick surge of moisture to affect the area. This will
again support moisture convergence and locally and diurnally
induced early morning and afternoon convection across portions of
the islands. Some of the afternoon convection over Puerto Rico
may be enhanced during the time of maximum heating particularly in
the west and northwest interior of Puerto Rico.
Improving weather conditions expected during the early at of next with
as high pressure builds aloft and the cap inversion strengthens once
again over the area....limiting convective development.
Aviation...mostly vcsh with brief periods of MVFR conditions in
rain showers expected until 05/14z across tncm...tkpk and across the eastern
taf sites of Puerto Rico and USVI...tist...tisx and tjsj as a weak
easterly wave will move across the flying area. Periods of rain showers/thunderstorms and rain
expected after 05/16z across several sectors in PR which will likely
cause thunderstorms in the vicinity for tjbq/tjmz/tjsj/tjps...as well as possibly affect the
actual station...causing MVFR conditions until 05/23z. Winds will be mainly
light and vrb this morning...becoming east-southeast at around 10kt with sea breeze
variations after 05/14z.
Marine....winds and seas are expected to remain tranquil but
may slightly increase near any convection accompanying the
easterly wave forecast to move across the region today through
early Sunday. Please refer to the latest coastal waters forecast
issued by the National Weather Service weather forecast office San Juan PR.
Preliminary point temps/pops...
sju 91 79 91 79 / 60 40 40 10
stt 88 80 89 80 / 50 40 40 20