Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Juan PR
420 am AST Wednesday Sep 17 2014
Synopsis...TUTT low north-northwest of the area will gradually fill and merge
with a deepening trough over eastern noam by Friday. Upper level ridge will
build on Friday. Another TUTT will establish over the area during the weekend
and early next week. A tropical wave is expected Thursday night-early
Friday with another tropical wave expected on Monday.
Discussion...considerable middle-high level cloudiness will advect
over the area today on a 50-knots wrly jet streak around the base of
TUTT low to the north which would tend to limit daytime heating
and convective development. In fact...GFS develops no precipitation at
all today and shows very little moisture between 850-500 mb today
which is confirmed by 06z CIRA layered precipitable water product.
Moisture begins to increase on Thursday afternoon with approach of
tropical wave along 57w. Most active weather will be Thursday night over
eastern PR...USVI...coastal waters and Friday over Mainland PR. While
moisture looks pretty decent...models still show hostile upper
level conditions. Drying is expected Friday night and Sat as wave
moves into the dom rep. Another wave currently analized along 37w will
approach the area late sun/early Monday with risk of showers
Aviation...VFR xptd except MVFR in scattered rain showers/thunderstorms and rain and obscured mountains northwest PR
this after. Isolated rain showers elsewhere today-Thursday morning but should remain VFR.
Wind below fl150 southeast 6-14 knots becoming east tonite-Thu.
Marine...seas mainly 2-4 feet. NE swells will begin to subside
today. A slight increase in winds expected Sat. Otherwise...winds
generally below 12 knots most of the 5-day period.
Preliminary point temps/pops...
sju 89 80 89 80 / 10 10 20 40
stt 82 81 82 82 / 10 10 30 40