Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service San Juan PR
254 PM AST sun Apr 20 2014

Synopsis...middle to upper level ridge will will continue to flatten/erode
across the region...as TUTT east and northeast of the Lesser Antilles
pulls farther north and weakens...while another short wave moves
eastward across the western Atlantic. This will leave a convergent
and high zonal/westerly wind flow aloft through at least Wednesday.
At the surface and low levels...strong high pressure ridge that
has been extending across the region in recent days will continue
to weaken and relax the local pressure gradient...as it pulls
farther north into the Atlantic and a polar trough and associated
cold front moves eastward across the western Atlantic through
Wednesday.

&&

Discussion...erosion of the ridge aloft will continue through
the early part of the week. Surface high pressure pulling father
north of region will allow for lighter trade winds and lesser
upper level support to enhance the low level moisture convergence
and passing trade wind shower that has been affecting the region in
recent days. Expect lesser activity overnight through Tuesday and
Wednesday...with mostly isolated passing showers to affect parts
of the east coastal sections of the islands....followed by isolated
to scattered afternoon convection during the day...over parts of
the islands.

By middle week...previously mentioned polar trough/weakening cold front
is to move across the west Atlantic and create an area of low level
convergence along with an induced prefrontal trough. This feature is
expected to affect the area on Wednesday and Thursday and should
bring an east southeast wind flow and moderate amounts of moisture
transport. This in turn will allow for better formation of early
morning showers along with some enhanced afternoon convection
which will be mainly forced by local/diurnal effects and sea and
land breeze convergence. In addition...recent Galvez-Davison index
as well as latest GFS model guidance all suggest best potential for
increasing moisture and more unstable conditions...should be during
the latter part of the upcoming week. Will continue to monitor and
see how this pattern unfolds.

&&

Aviation...rain showers decr most of region. But rain showers WI MVFR ceilings to
persist this after near tjsj/tjbq and possible tjmz...few obscured mountains othw
VFR except rain showers reaching tncm/tkpk again tonite. Wind east-southeast 12-18 knots becoming
southeast 10-15 on Monday. Fl100-fl200 to be variable/less than 10 knots.

&&

Marine...winds and sea heights continued to decline across the as
expected with continued diminishing winds expected across the region
over the next few days. Recent buoy data from 41043 suggests seas
around 7 feet or so with a slow but steady decline noted in recent
hours. The near shore buoy 41052 suggest seas of 5 to 6 feet and slow
decline. Seas are no longer expected to be at Small Craft Advisory
criteria within the regional waters...therefore small craft
advisories have been cancelled or allowed to expire. However due to
moderate to locally fresh trade winds small craft operators should
exercise caution for most of the local waters. Please refer to the
latest coastal waters forecast issued by the weather forecast office National Weather
Service San Juan.

&&

Preliminary point temps/pops...
sju 77 88 75 87 / 20 20 10 40
stt 76 86 77 87 / 30 20 20 50

&&

Sju watches/warnings/advisories...
PR...none.
Vi...none.
Coastal waters...none.
&&

$$

54/09