Latest AFD San Juan about effects from 91L/Otto?? in PR/VI

[cycloneye]

fxca62 tjsj 091954 cca
afdsju

puerto rico and u. s. virgin islands forecast discussion
national weather service san juan pr
350 pm ast tue nov 9 2004

. synopsis ... at upper levels ... the upper level trough was over
eastern cuba at 12z and has southwest winds on its eastern flank of
80 knots over the southern bahamas. strong divergence now appears
south of hispaniola. over the next 24 to 36 hours the jet will move
slowly east and the area of strong divergence aloft will move over
puerto rico and the u. s. virgin islands. although the jet lags
behind over hispaniola until sunday little or no divergence is seen
after thursday morning until monday morning. the trough passes
monday night and flow becomes westerly through thursday.

at mid levels ... a strong trough that has dropped in over cuba
remains over the windward passage even while the trough becomes more
positively tilted. it resumes an eastward movement ... but becomes
very weak during the weekend. from the beginning of next week high
pressure ridges in across hispaniola and the bahamas ... then rotates
from a negative tilt to a positive tilt.

at lower levels ... a trough extends from the pacific ocean near the
gulf of panama to a low near 15 north 72 degrees west and then to
another low near 22 north 66 west and farther north to a low near 40
north 57 west. the low near 15 north 72 west is forecast to develop
and move parallel to the coast about 40 miles south of puerto rico
thursday night and friday. this low will move northeast of the area
during the weekend and drier air will filter in.

&&

. discussion ... slightly drier surface air burrowed under our moist
air mass last night as evidenced by slightly lower dewpoints and
north winds in san juan and later saint thomas. this held the
convection at bay to our south. apparently this was too
insignificant a feature to be picked up by the gfs yesterday or
today ... but certainly significant enough to affect the coverage of
rainfall for puerto rico. thus puerto rico had sketchy rain
overnight while amounts were substantial over the u. s. virgin
islands.

yesterday it was unclear how the trough would spawn low pressure
systems that it was developing along its length. todays models are
developing the system that is south of haiti and bring it directly
toward the island until wednesday night ... when it changes course to
almost due east and passes about 40 miles south of puerto ricos
southern coast. models show significant moisture beginning around
22z tonight over most of the island and continuing more or less
steadily through wednesday night. the strongest upward vertical
motion and best relative humidity are still forecast to occur
wednesday around 8 pm ast ... however heavy rainfall will likely begin
much earlier. if the low pressure develops according to the model
solution ... northeasterly flow over the area should begin before
midnight tonight causing strong convergence at the surface and the
beginning of a broad area of upward motion over the area.

factors of uncertainty include the speed and direction of the low
pressure system ... the amount that it develops and whether it passes
south or over the area. nevertheless ... confidence is growing that
the system will pass south of puerto rico and just miss saint croix.
current position estimate by the national hurricane center are for
the low to move slowly to a position of 17. 3 north 69. 9 west at
11/00z or 181 miles west southwest of cabo rojo ... and then
accelerate and move to a position of 17. 6 north 67. 0 west or about
29 miles southeast of cabo rojo at 11/12z or 8 am ast ... and then
move slowly during the next 24 hours to a position of 17. 6 north
64. 5 west ... or about 18 miles southeast of saint croix.

although this system is expected to bring much more rain than
wind ... winds could reach 30 mph sustained in some areas of the west
coast and perhaps 30 to 35 knots in the mona passage as early as
wednesday afternoon.

temperature forecasts look on track at this time ... maximums are
below normal through much of the week ... but will lower max for
wednesday and thursday one more time.

&&

. hydrology ... models are showing substantial moisture beginning
tonight and lasting through thursday ... with the most intense
dynamics passing over puerto rico on wednesday afternoon. we are
expecting amounts of 4 to 8 inches over the island during the period
8 pm tonight to 8 pm wednesday night. higher amounts could be
experienced on the favored side of higher terrain. conditions for
heavy rainfall look most favorable on wednesday afternoon ... but
could begin happening as early as tonight over local parts of puerto
rico ... particularly west puerto rico and the virgin islands.
unofficial observations from saint croix show one and three quarters
of an inch since midnight already.

&&

. marine ... marine model forecasts have adjusted slightly upward after
making a large correction downward for the swell out of the
atlantic. so will stay with 10 to 12 foot swell ... ramping up
thursday and continuing friday and saturday. another very large
event is being forecast on tuesday of next week for the atlantic.

wind waves will be of considerable concern during the passage of the
eastern caribbean low on thursday south of puerto rico and saint
croix as well as in the mona passage. waves could rise quickly to 6
to 8 feet as early as wednesday night and continue through thursday.

areas of the south coast could experience some minor coastal
flooding ... but would like to see the winds develop around the low
toward us rather than to the east as currently being observed before
actually issuing a watch for coastal flooding on the south coast.
coastal flooding remains a possibility later in the week for the
north coast from the north swell there thursday and friday.

This is why this NWS office is one of the best around the US when discussions are issued.Wow a complete panoramic view of all the scenarios for Puerto Rico and the Virgin Islands.

[tronbunny]

Luis, this is a great discussion.
Looks a little less menacing for you.

I agree that it's very detailed and informative.
Thanks for sharing.

[cycloneye]

My worrie is about the movement that is slow now because it may cause massive flooding here.

[msbee]

this thing may cause more problems than we think

[HURAKAN]

RAINS CONTINUE TO GET CLOSER TO PUERTO RICO, HEAVY RAIN CAN BE EXPECTED IN A FEW HOURS