Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service San Juan PR
907 PM AST Friday Nov 28 2014
Update...showers west of Saint Croix and around Saint Thomas continue
to edge closer to the East Coast of Puerto Rico. A few have even
developed over Hatillo and moved into Camuy. Showers will be brief and
heavy amounts are not expected. An area of moisture is advancing
toward Puerto Rico. Precipitable water values over Saint Croix
have surpassed 1.7 inches now and will rise a little more
Discussion...models show less turning of the winds toward the
northeast during the day tomorrow...and 29/00z sounding showed
south winds from 6 to 14 kft. Winds were calm between 3 and 6 kft
and easterly below that with some land breeze influence. Have
raised some probability of precipitation over Puerto Rico for tomorrow for overall risk of
showers but amounts should remain limited. Best rain should be
over higher terrain. Model moisture is also increasing and the
very dry air found in the 29/00z sounding above 800 mb will
moisten considerably in the next 18 hours. Otherwise no changes
Aviation...mainly VFR conditions expected through the forecast
period. However...passing rain showers between Leeward Islands and eastern
PR will result in vcsh across tjps/tist/tisx/tncm/tkpk with possible
brief MVFR ceilings. Light and variable winds overnight...after 29/12z
east-NE surface winds at 5 to 10 knots with sea breeze variations.
Marine...seas are still forecast to rise to 7 feet in
amz710...Atlantic offshore waters...beginning early Monday in
response to north northwest swell and increasing winds.
Previous discussion... /issued 222 PM AST Friday Nov 28 2014/
Synopsis...ridge aloft will flatten tonight and Saturday as polar
trough moves across the western Atlantic. Surface high will build
across the western Atlantic early next week...tightening the local
Discussion...mostly sunny skies prevailed across the local islands
through the day...with few sprinkles observed across the Caribbean
waters and Saint Croix. Temperatures were in the middle to upper 80s
at lower elevations and near 80 degrees at higher elevations.
A generally fair and mainly stable weather pattern will prevail
across the local islands through early Saturday morning...under
upper level ridge and associated subsidence inversion. Moisture
advection is then expected late Saturday morning and into Sunday
under weakening ridge. Therefore...expect a few passing showers
across the Caribbean waters...U.S. Virgin Islands and eastern
Puerto Rico tonight...becoming isolated to locally scattered
in the morning hours on Saturday. Under moisture advection and
weakening subsidence inversion...showers with an isolated
thunderstorm or two will develop across portions of the Cordillera
Central Saturday afternoon as well. A similar weather pattern is
expected Sunday with early morning passing showers across U.S.
Virgin Islands and eastern Puerto Rico followed by afternoon
showers and an isolated thunderstorm or two over the Cordillera.
Early next week as surface high builds across the western Atlantic...
trades will strengthen across the local area. This will enhance low
level moisture transport from the east northeast...resulting in the
continued trend of passing showers across the north and east coastal
sections of local islands Monday through at least Wednesday. A 20
knots wind flow will also inhibit sea breeze development as well as
afternoon showers during that time frame.
A broad surface trough and associated area of low pressure will
develop across the Caribbean by the end of the next workweek...
promoting significant moisture transport into the region with the
risk heavy rainfall Thursday through the end of the week.
Aviation...VFR conds and partly cloudy skies will prevail during
the next 24 hours at all taf sites. Few brief passing rain showers moving
mainly in/around tjmz/tjbq/tncm/tkpk. Also...shra/tsra possible
over the Caribbean waters. Easterly surface wind at 5 to 15 miles per hour with
local sea breeze variations along coastal taf sites until 28/22z
dropping light and variable overnight. The chance of rain showers/thunderstorms and rain
will increase tonight into Sat as moisture content is expected
to increase across the local area.
Marine...light trade winds will prevail tonight but gradually
strengthening Saturday into Monday as a high pressure builds
across the western Atlantic. Northwest to north swells expected
to reach the Atlantic coastal waters Sunday into Monday with
Preliminary point temps/pops...
sju 74 85 74 85 / 30 40 30 40
stt 77 86 77 86 / 40 40 40 40