Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Juan PR
940 PM AST sun Nov 23 2014
Update...overall drier conditions prevailed today with mostly fair
weather skies dominating much of the islands. Few passing showers
affected parts of the islands from time to time but the fairly
strong easterly trade winds continued to push the cloud fragments
and accompanying shower activity quickly westward leaving little
rainfall accumulations. Latest tjsj 24/00z upper air sounding
showed precipitable water down to 1.42 inches this evening as a
slot of drier air filtered in from the east and high pressure
continue to build aloft across the region. However satellite
imagery and the evening sounding from tffr (guadeloupe) showed
another surge of low to middle level moisture now crossing the Lesser
Antilles...with a slight increase in precipitable water value to near 1.88
inches. Expect the strong easterly trade to transport this
moisture towards the region during the overnight and morning
hours. So expected another round of showers to affect the coastal
waters and east coastal sections of the islands overnight through
Monday morning. Otherwise no changes made to the inherited
forecast package at this time.
Aviation update...VFR conditions expected across all the taf sites
through the forecast period. Passing -shra and vcsh likely across
the leeward/USVI terminals and possibly tjsj overnight. Tjsj 00z
radiosonde observation indicated deep easterly flow at 15-25 knots below fl250.
Marine update...latest data obtained from the local and offshore buoys
as well as satellite derived wind data and a few ship observations all
suggest fresh to strong easterly trade winds continued across the
regional waters...with wind driven seas up to near 8 feet offshore.
Expect these conditions to continue until at least Wednesday and
therefore maintain rough and hazardous sea conditions.
Previous discussion... /issued 239 PM AST sun Nov 23 2014/
Synopsis...upper level ridge will build across the region next
several days. At the surface...strong high pressure north of the
area...will continue to produce fresh to strong trade winds across
the region. Patches of low level moisture will move across the
region from time to time.
Discussion...pleasant weather conditions were observed this afternoon over
Puerto Rico and the U.S. Virgin Islands. A dry air mass has moved
across the region...limiting the shower activity across the area.
Only light passing showers were observed. Upper level ridge is in
total control of the weather locally. This ridge is expected to
maintain relatively dry conditions across the region through most
of the week. Computer models suggest Tuesday will be the wettest
day as an area of moisture moves through the area.
Strong high pressure at the surface will maintain strong trade
winds across the region through middle week. These winds will
continue to transport patches of low level moisture from time
time...affecting the local islands. However...no significant
rainfall accumulations are expected as these showers will move
Aviation...mostly VFR conditions are expected across the local
flying area tonight with only vcsh. Latest tjsj sounding indicated
an easterly wind flow up to 30 knots all the way from the surface to
10k feet...becoming light and variable aloft.
Marine...fresh to strong easterly trade winds will continue across
the regional waters through at least Tuesday...and therefore
maintain rough and hazardous seas. Small craft advisories remain
in effect for all coastal waters except for the near shore coastal
waters of southwest PR. Please refer to the latest marine weather
statements and coastal waters forecast issued by the National
Weather Service weather forecast office San Juan PR.
Preliminary point temps/pops...
sju 76 85 76 85 / 30 30 40 40
stt 78 89 79 88 / 30 30 40 40
Coastal waters...Small Craft Advisory until 6 PM AST Wednesday for Anegada
Passage southward to 17n-Atlantic waters of Puerto Rico and
USVI from 10nm to 19.5n-Caribbean waters of Puerto Rico
from 10 nm to 17n-coastal waters of northern Puerto Rico
out 10 nm-coastal waters of northern USVI and Culebra out
10 nm-coastal waters of southern USVI Vieques and eastern
Puerto Rico out 10 nm-Mona Passage southward to 17n.
Small Craft Advisory until 6 am AST Tuesday for coastal waters
of southern Puerto Rico out 10 nm.
Small Craft Advisory from 6 am to noon AST Wednesday for coastal
waters of southern Puerto Rico out 10 nm.
Small Craft Advisory until 6 PM AST Tuesday for coastal waters
of northwestern Puerto Rico out 10 nm.