Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Juan PR
1030 PM AST Friday may 22 2015
Update...a few showers developed across the northwestern
municipalities of PR early in the evening. These were relatively
short lived and did not produce any flooding.
Hazy skies were observed today due to Saharan dust and it is
expected to continue hazy for the next few days as Saharan dust
remains over the area. Latest guidance suggests that available
moisture will remain fairly constant with precipitation-water values at
around 1.6 inches. So there is a slight chance of brief showers
overnight and in the morning hours with a chance of showers across
western PR in the afternoons for the next several days.
Latest naaps aerosol guidance suggests that we will have at least
light concentrations of dust until Tuesday...so relatively dry
conditions are expected across the local area at least until then.
However in the long range...the GFS and the European model (ecmwf) models continue to
insist that a tropical wave will reach the local area on
Wednesday...with the bulk of the moisture reaching the local area
in the latter part of the week. Of course this is in the very long
range and there is a great deal of uncertainty.
Aviation...VFR conds expected through the forecast period. Winds
light and variable overnight...becoming easterly with sea breeze
variations at about 15 knots...after 23/12z. Some rain showers/vcsh developing
around tjmz/tjbq after 23/16z. No sig weather forecast en Route by the way islands
excpt for haze.
Marine...the local buoys are reporting seas of 4 feet or less
with winds under 15 knots. Seas are expected to increase
slightly...up to 5 feet overnight across the offshore waters.
Previous discussion... /issued 258 PM AST Friday may 22 2015/
aloft...the islands lies between a trough to the north and a ridge
to the south. By Tuesday...an upper level trough will build off
to the northeast of the local area. A middle level ridge will move
across eastern Caribbean through Sunday...followed by a middle level
trough. A Saharan air layer will continue moving across the
eastern Caribbean throughout the weekend.
latest model forecast and observations along with recent tjsj radiosonde observation
data continue to suggest the spreading of a Saharan air layer
across eastern Caribbean. Additionally...a sub tropical jet aloft
will continue to push high clouds into the region this afternoon
and tonight. Therefore...limited convective shower activity is
expected during that period...most of the activity...if any will
be across the interior and western sections of the islands.
Moderate trade winds and hazy conditions are expected to prevail
across the local area today. A similar pattern is expected
throughout the weekend across the local area...with nocturnal trade
wind passing showers across the eastern sections of PR...the USVI
and their surrounding waters...and afternoon convection across
western Puerto Rico each day.
For early next week...moisture is expected to increase and typical
trade wind pattern and afternoon convection with T-storms across
western PR will establish once again across the islands. The
operational models continue to suggest increasing tropical
moisture by the latter portions of the upcoming week.
Aviation...VFR conds for PR/USVI xcpt brief local MVFR in rain showers/isolated
thunderstorms and rain by the way 18z-22z today and Sat mainly over western PR... few obscure mountain top
over due to rain showers/possible -tsra. Scattered-broken low cloud layers by the way fl020- fl050.
Wind from southeast 10-15 kts below fl200...becoming from west above and increase west/heat maximum wind
65-70 kts near fl450. No sig weather forecast en Route by the way islands excpt for
slight haze aloft.
Marine...Ponce buoy is indicating wind driving waves up to five
feet...among that...the local buoy network continues to indicate
fairly tranquil seas of 5 feet or less and winds at 15 to 20
Preliminary point temps/pops...
sju 76 91 76 88 / 10 20 20 20
stt 78 89 77 87 / 20 20 20 20