Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service San Juan PR
503 am AST Friday Aug 1 2014
Synopsis...TUTT low north of the area will retrogress toward the
Bahamas tonight. Ts Bertha expected to pass south of Ponce Sat
afternoon bringing beneficial rains to most of the region.
Discussion...TUTT will maintain unstable conditions today but
subsidence and drying ahead of ts Bertha will limit shower covering
this afternoon. Fair weather expected this evening ahead of
Bertha. Showers and squalls will begin to affect the USVI after
06z Sat reaching eastern PR around daybreak Sat. Rain heavy at times
expected Saturday as Bertha tracks west-northwest south of Ponce around 20
miles per hour. Heaviest rainfall accumulations of up to 6 inches are
possible over favored topographic regions of El Yunque and Cayey
mountain ranges. Rest of PR and USVI will likely see amounts in the
1 to 3 inch range with southwest PR likely to see the least amount
of rain. Still cloudy and showery Sat night but areal coverage and
intensity of showers will decrease as middle-level circulation moves
past PR. Isolated tornadoes will also be possible in squalls and
embedded in rain bands once surface winds shift to the southeast Sat
afternoon. Gusts to tropical storm force can also be expected
Saturday especially over higher elevations and in squalls and rain bands.
Things dry out quickly Sunday with a very nice day on tap. Upper
level ridge strengthens through all of next week with overall very
Aviation...VFR conds will prevail at all taf sites through the forecast
period with vcsh at tjsj/tist/tisx and tncm in the morning hours.
Between 01/17-01/21z brief MVFR ceilings possible due isolated-scattered rain showers/thunderstorms and rain
developing across the northwestern section of PR and affecting tjbq
and tjmz. East-southeast winds 10 to 20 kts below fl100. Tropical storm
conditions expected Saturday.
Marine...sustained winds 25-30kt with gusts 35-40 knots. Seas 7 to 9
feet Saturday. Winds and seas begin to improve rapidly Sat night.
Fire weather...before the rains arrive late tonight very dry air
will move in over St. Croix later today with red flag conditions
expected. Vieques had some decent rains yesterday with up to 0.62
inches so will not issue an rfw for them. The very dry air will
not make it on time to Mainland PR so no red flag conditions
Hydrology...widespread amounts of one to three inches with up to
six inches possible in favored topographical regions of the Cayey
and Luquillo mountain ranges are expected Saturday with the
passage of Bertha. Very low stream flows and drought conditions
will preclude the issuance of a Flash Flood Watch but heavy rains
can have quick impacts on rivers in northeast PR due to their
short length and steep slopes.
Preliminary point temps/pops...
sju 91 81 82 78 / 20 100 100 90
stt 89 79 81 80 / 10 100 100 90
PR...Tropical Storm Warning for central interior-Culebra-eastern
interior-Mayaguez and vicinity-north Central-Northeast-
northwest-Ponce and vicinity-San Juan and vicinity-
Vi...Tropical Storm Warning for St Croix-St. Thomas/St. John/adjacent
Red flag warning from 9 am this morning to 5 PM AST this
afternoon for St Croix.