Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Juan PR
510 am AST Tuesday Apr 21 2015
Synopsis...a weak upper level trough will move close to the
region today. A middle to upper level ridge will then build over the
region until at least the end of the week. A weak surface high
pressure over the central Atlantic will maintain a moderate trade
wind flow across the region.
Discussion...Doppler weather radar detected isolated to scattered
showers mostly across the surrounding coastal waters overnight
and early this morning. Under an east southeast low level wind
flow...some of these showers affected the eastern and southeastern
sections of Puerto Rico as well as parts of the U.S. Virgin
Islands. Not precipitation was detected elsewhere over the local
islands so far this morning.
The east southeast trades winds will continue to transport small
patches of tropical moisture across the local islands today and
through the end of the week. These showers will continue to affect
the eastern sections of Puerto Rico during the rest of the
morning hours...but only isolated passing showers afe expected at
this time. A weak upper level trough will move close to the region
today. Thus...for the afternoon hours...this trough is expected
to combine with the limited available moisture...daytime heating
and local islands effects to induce the development of scattered
showers and a couple of thunderstorms across interior and western
parts of Puerto Rico. This activity will diminish rapidly after
sunset. No major changes are expected in the present weather
regime in the foreseable future.
Aviation...VFR conds expected through the forecast period. However...from
21/17-21z...shra/isold thunderstorms and rain possible over the interior and western
sections of PR. This may lead to brief mountain tops obscr and MVFR
conds...affecting mainly tjmz and vcty. Light/vrb surface winds overnight
until 21/14z...then becoming from the east kts 10-15kts with higher gusts
and sea breeze variations.
Marine...buoy 41043 to the north of the local area is now
reporting seas under 5 feet. Therefore we expect seas mainly of 4
feet across the local Atlantic waters with occasional moments of 5
feet. The trend is for seas to continue mainly 2 to 4 feet with
occasional moments of 5 feet for the next few days. Northeasterly
swell is forecast to invade the local waters on Thursday...
increasing seas to 6 feet across the local Atlantic waters.
Preliminary point temps/pops...
sju 89 75 88 76 / 20 10 20 20
stt 85 75 85 77 / 20 20 20 20