Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Juan PR
315 PM AST Wednesday Sep 17 2014
Synopsis...TUTT across the western Atlantic into the Greater
Antilles will weaken over the next few days as a deeper trough
amplifies over the eastern coast of USA. Trofiness aloft will
return once again early next week as another TUTT develops across
the central Atlantic into the eastern Caribbean. Next tropical
wave passage expected late Thursday into Friday.
Discussion...TUTT low northwest of the area will weaken as deep
polar trough establishes across the eastern USA. Meanwhile at middle
levels...weakening of middle level ridge pattern continues tonight
and tomorrow. Middle level ridge pattern is sustaining a weak cap
across the local islands. The aforementioned cap and limited low
level moisture across the area are helping to suppress significant
shower and thunderstorm activity this afternoon. Although...afternoon
convection cant be ruled out later this afternoon.
Moisture associated with approaching tropical wave...now located
near 59w...will reach the local islands as soon as Thursday
afternoon. Model guidance continues to suggest most active weather
Thursday night and early Friday morning over eastern Puerto Rico
and USVI spreading across western Puerto Rico Friday afternoon.
A drier air mass is expected to move in from the east Friday night
and Saturday as the wave moves further west into the Mona Passage
and Dominican Republic. Another wave currently localized near 39w
will approach the area late Sunday/early Monday with risk of showers
Aviation...VFR conds expected for all taf sites except for possible
brief rain showers that could affect tjmz by mid-afternoon. Isolated vcsh
possible for local islands through the night. Wind below fl070 east 6-14 kts
becoming southeast above fl080 at 5-10 kts.
Marine...seas mainly 2-5 feet. NE swells will begin to subside
tonight. A slight increase in winds expected Sat. Otherwise...
winds generally below 17 knots most of the 5-day period.
Preliminary point temps/pops...
sju 80 89 80 88 / 20 20 60 60
stt 78 89 78 89 / 20 30 60 60