Another long AFD from NWS San Juan about scenarios of low

[cycloneye]

fxca62 tjsj 082012
afdsju

puerto rico and u. s. virgin islands forecast discussion
national weather service san juan pr
350 pm ast mon nov 8 2004

. synopsis ... at upper levels ... flow has split over the central united
states with one leg of the jet extending from arkansas to western
cuba and turning northeast over the windward passage. this southwest
flow continues and edges into hispaniola through thursday. an area
of good divergence aloft is present over puerto rico tuesday night
through wednesday evening. the jet then moves eastward over puerto
rico on saturday ... followed closely by the passage of the upper
level trough on sunday. upper level flow is then predominately from
the west through the following thursday.

at mid levels ... a strong trough has developed over cuba and will
move slowly eastward during the week ... passing puerto rico late
saturday night. high pressure develops over the entire caribbean
from sunday through the end of the following week.

at lower levels ... a trough has developed from panama and colombia
that extends to lows east of florida ... north of hispaniola and
farther north over the northwest atlantic. strong high pressure is
in the north central atlantic and over the mid western united
states. high pressure over the united states will push cooler and
drier air towards the local area and create a robust boundary
between warm moist air and the cooler though still somewhat moist
air. the trough will become more and more positively tilted and low
pressure systems will develop within it and move northeast along the
trough. the trough will slowly shift eastward toward puerto rico and
become more positively tilted at the same time.

&&

. discussion ... the current radar picture shows convective activity
growing over the northwestern third of the island while rain
continues over the coastal sections of the southeast. some shower
activity is also noted over the u. s. virgin islands. currently
showers are moving in from the south south east and are reflecting
the low level flow perhaps even more than the actual surface flow.
precipitable water over isabela has been increasing most of the day.

models show moisture increasing overnight through 06z ... with slight
drying until mid morning tuesday. the gfs shows an area of strong
omega forcing during the day tuesday as the patch of higher relative
humidity moves through and so showers and thunderstorms should be
numerous during this time with copious rainfall from place to place.

models do not completely agree on the position or nature of the low
pressures that are to form in the trough as it passes through. some
model runs in the past 24 hours have had a series of weak lows
moving northeast along the trough ... each with its own little wind
circulation and these pass near puerto rico. other runs have had one
larger circulation forming south of hispaniola that moves slowly
toward the area and passes through thursday and friday. that models
have such a mixture of winds at the surface from midday tuesday
through thursday highlights the uncertainty of the forecast and
shows how little we will be able to rely on any single solution
showing an exact position of any particular low or wind flow around
it or amount of relative humidity in the vicinity.
nevertheless ... while exact amounts of rain cannot be
pinpointed ... amounts will be significant and rainy conditions will
continue at least through thursday and possibly through saturday.
since the upper level trough does not pass until saturday conditions
will be somewhat favorable to heavy rainfall each day until then.
the exact location will depend on the wind direction and the
position of puerto rico with respect to the individual lows that
pass nearby and the size and strength of those lows. rainfall in the
virgin islands will be above normal but at this time the amount of
heavy rain will be considerably less than over the main island of
puerto rico.

temperatures will be a little below normal during the period. some
of the high temperatures forecast may be a little high ... should
conditions become cloudier than expected or wetter for longer
periods.

&&

. hydrology ... with conditions worsening with respect to the
possibility of heavy rain across the area ... some considerable
attention has been given to the issuance of a flood watch.
discussion has centered around the timing rather than around whether
one would be needed since it was universally agreed that some
flooding will occur. rain will not occur continuously during the
period though it may occur at any time during the period. rainfall
amounts could be especially heavy ... however... during the mid
afternoon hours tuesday and wednesday with amounts of 4 to 8 inches
possible in favored areas ... and higher amounts in local areas
between noon on tuesday and dawn thursday morning. for this reason a
flash flood watch will be issued this afternoon for the period
between noon tuesday and 6 am ast thursday. rainfall is expected to
be heavier wednesday than tomorrow.

&&

. marine ... a combination of strong pressure gradients and long fetch
areas will send high waves into the local area from the north
beginning on thursday and continuing through saturday. earlier
models have had wave heights as high as 14 feet arriving in our
atlantic waters on friday ... but later runs have backed off to only
10 feet. seas will not likely be much less than this however as
larger bullseyes were present in waters north of the dominican
republic. this means that breakers of at least 12 feet and
occasionally 18 feet could be possible by late thursday and friday.

Again another educational,informative and long discussion from the NWS at San Juan about what may happen with the troughs that will move thru the caribbean with lows embedded.

[cycloneye]

SERVICIO NACIONAL DE METEOROLOGIA SAN JUAN PR
325 PM AST LUNES 8 DE NOVIEMBRE DE 2004

...EN EFECTO VIGILANCIA DE INUNDACIONES PARA LA TARDE DEL MARTES
HASTA LA MANANA DEL JUEVES...

LA VIGILANCIA INCLUYE LAS SIGUIENTES AREAS...

EN PUERTO RICO...
TODO LA ISLA GRANDE DE PUERTO RICO

EL ALTO CONTENIDO DE HUMEDAD Y EL INCREMENTO EN CONDICIONES
ATMOSFERICAS FAVORABLES ESTAN DANDO PASO A POSIBLES INUNDACIONES
REPENTINAS A TRAVES DE PUERTO RICO...COMENZANDO MARTES Y CONTINUANDO
HASTA AL MENOS JUEVES EN LA MANANA. LOS INDICIOS SON QUE EL PELIGRO
MAYOR PARA INUNDACIONES REPENTINAS OCURRIRA DURANTE EL MIERCOLES.
ACUMULACIONES TOTALES DE 4 A 8 PULGADAS SON ANTICIPADAS...CON
CANTIDADES LOCALES MAS ALTOS POSIBLES.

UNA VIGILANCIA DE INUNDACIONES PARA INUNDACIONES REPENTINAS
SIGNIFICA QUE LAS CONDICIONES SON FAVORABLES PARA LLUVIAS FUERTES A
TRAVES DEL AREA BAJO VIGILANCIA...LO CUAL PODRIA PRODUCIR
INUNDACIONES A CORTO PLAZO. SI USTED SE ENCUENTRA EN EL AREA BAJO
VIGILANCIA...COTEJE SUS PLANES DE EMERGENCIA....ESPECIALMENTE SI
TIENE INTERESES A LO LARGO DEL AREA DE LOS RIOS. MANTENGASE
INFORMADO Y ESTE LISTO PARA TOMAR ACCION RAPIDA SI SE OBSERVAN
INUNDACIONES O SI SE EMITE UN AVISO.

MANTENGASE ENSINTONIA CON RADIO NOAA...O LOS MEDIOS NOTICIOSOS
LOCALES...PARA LA INFORMACION MAS ACTUALIZADA SOBRE ESTA SITUACION.

ESTE PRODUCTO...AL IGUAL QUE OTROS PRODUCTOS HIDROLOGICOS E
INFORMACION CLIMATOLOGICA ESTA DISPONIBLE EN LA PAGINA DEL INTERNET
HTTP://WWW.SRH.NOAA.GOV/SJU O EN HTTP://WEATHER.GOV.

This is in spanish but the NWS in San Juan has issued a flash flood watch for all of Puerto Rico from tuesday afternoon until thursday morning.From this event of bad weather from this low pressure trough we expect 4-8 inches with some rainfall totals more higher than that.

[cycloneye]

CARIBBEAN...
A STRONG MIDDLE TO UPPER LEVEL TROUGH LOCATED OVER THE BAHAMAS
EXTENDS SWD ACROSS W CUBA AND THE NW CARIBBEAN INTO CENTRAL
AMERICA NEAR THE GULF OF HONDURAS. SUBSIDENCE AND VERY DRY
MIDDLE TO UPPER LEVEL AIR W OF THE TROUGH IS PRODUCING A
DRY/STABLE ENVIRONMENT. EAST OF THE TROUGH...A LARGE PLUME OF
DEEP LAYERED TROPICAL MOISTURE IS SURGING NWD OVER THE CENTRAL
AND E CARIBBEAN INTO THE CENTRAL ATLC. THIS COMBINED WITH BROAD
UPPER LEVEL DIFFLUENT FLOW IS PRODUCING A LARGE AREA OF
CLOUDINESS AND SCATTERED SHOWERS/THUNDERSTORMS FROM THE SW
CARIBBEAN NEWD OVER HISPANIOLA AND PUERTO RICO. MOST OF THIS
ACTIVITY IS FOCUSED WITHIN 250 NM EAST OF A SURFACE TROUGH
EXTENDING FROM W HISPANIOLA SWD TO COSTA RICA. AN ILL-DEFINED
1006 MB LOW HAS FORMED ALONG THE TROUGH NEAR 12N77W BUT
UPPER-LEVEL WINDS ARE CURRENTLY NOT FAVORABLE FOR TROPICAL
CYCLONE DEVELOPMENT. NONETHELESS...THE LOW IS ENHANCING
ENHANCING DEEP CONVECTION AND WILL PRODUCE LOCALLY HEAVY
RAINFALL OVER HISPANIOLA AND PUERTO RICO TONIGHT AND TOMORROW AS
IT LIFTS QUICKLY NEWD.

A low has formed but upper conditions are not favorable for tropical cyclone formation however are favorable for copius amounts of rain to fall at Hispanola and Puerto Rico and adjacent islands.