Scientific Forecaster Discussion
fxca62 tjsj 170850
Area forecast discussion
National Weather Service San Juan PR
450 am AST Fri Nov 17 2017
Synopsis...a frontal boundary is expected to remain very close
to the region through the upcoming weekend to result in periods
of showers and thunderstorms. A mainly fair and stable weather
pattern is expected next week as a mid to upper level ridge
builds across the area.
Short term...today through Sunday...
As the frontal boundary stalls to the west and north of the local
area, mostly cloudy skies, rain and isolated thunderstorms are to be
expected across the local area through the weekend. The latest
guidance is suggesting above normal moisture through the weekend and
the 17/00z radiosonde observation confirmed what guidance is suggesting by observing a
precipitable water value of 2.25 inches. Not the usual rain pattern
is expected with the current setup since we have mainly a southerly
wind flow with areas of SW wind component and somewhat light at
about 10mph or maybe even lighter, so there may be advective showers
and thunderstorms over the area which may be enhanced over land
areas. Bottom line is that most of the local area will observe off
and on showers with the occasional thunderstorm, especially over the
local waters, portions of the USVI and eastern PR under variably to
mostly cloudy skies through the weekend. The cloudiness and rain may
keep the daytime Max temperatures across the lower elevations in the
mid 80s, especially for Saturday and Sunday, upper 80s today.
Long term...Monday through Saturday...
A mid to upper level ridge is expected to build across the forecast
area early next week and hold much of the forecast period. As this
feature strengthens Mon-Tue, available low level moisture is
expected to quickly erode with precipitable water values remaining
below the normal range Tue-Fri. At lower levels, east to east
southeast winds will prevail across the local isles as a surface
high dominates the central Atlantic. Under the aforementioned
pattern, expect mainly fair and stable weather condition much of
the next week with trade wind showers across USVI and east PR as well
as some locally induced afternoon showers across west areas of
Aviation...shra/tsra activity is expected to increase across the
local area today, causing vcsh/thunderstorms in the vicinity across the local terminals today
with tempo MVFR conds possible. Ceilings will be mainly above fl100
before 17/10z but thereafter there will be moments of ceilings at fl060
and at times close to fl030, especially at tjbq, tjmz and tjps.
Winds will be mainly southerly with a SW component, generally at
10kt or less but gusty near thunderstorms and rain.
Marine...tranquil marine conditions will continue to prevail
across the local waters during the next several days with seas
up to 5 feet. Winds to continue from the south at 10 to 15 knots.
Preliminary point temps/pops...
sju 89 77 86 78 / 60 40 60 60
stt 86 79 86 79 / 60 50 40 60
PR...Flash Flood Watch until 2 PM AST this afternoon for northwest-