911 
fxca62 tjsj 282009 
afdsju 


Area forecast discussion 
National Weather Service San Juan PR 
409 PM AST Thursday Aug 28 2008 


Discussion...upper low just to the north of local area this 
afternoon has again enhanced diurnal convection across PR...and in 
the rainbands streaming southward off of the vi. This TUTT low is 
forecast to gradually shift westward beginning tomorrow...and currently 
remains nearly stationary...trapped in a middle level Omega block 
across the region. A very weak north-northwest to northwest steering flow exits this 
afternoon and will maintain very slow and limited storm motion 
through the evening hours. A second round of diurnal thunderstorms 
developed across the northwest slopes of PR in outflow boundaries from 
earlier activity and will linger across the west and northwest through 6 
PM. For tonight and Friday...local weather will be initiated and 
controlled by the precise low level wind flow induced by the passing 
circulation of T.S. Hanna. I like the GFS-CMC ensemble consensus 
track of a continued west-northwest motion for another 6-12 hours before 
making a marked northwest turn over the next few days. TUTT low continues 
to shear the llcl of Hanna strongly this afternoon...with the llcl 
being completely exposed all afternoon. A very small and tight 
center has been rotating around the central core of Hanna...with a 
mean motion of the core around 280-290 at 11 knots. Hanna will 
continued to be sheared and intensification is unlikely until the 
llcl moves northwest and under the NE quadrant of the TUTT low 
circulation...which will likely not occur inside the next 24 
hours. Convergence lines on the S and SW quads of the broader 
circulation will affect the local Atlantic waters...the north 
leewards...and possibly the Virgin Islands during the next 12 to 
18 hours before lifting out of the area. A weak SW to S low level flow 
is expected by tomorrow afternoon...with diurnal convection expected to 
develop along the north slopes and move NE. Drier more stable 
air...and eventually sal...and then expected to move into the 
region over the weekend...with east-southeast to southeasterly low level flow for more 
predictable and typical weather cycles. 


Global models still forecasting good organization and potential 
intensification of most of the next several tropical waves to move 
off of Africa...and thus all interests in the east and northeast 
Caribbean are urged to keep abreast of the tropics during the next 
few weeks as we rapidly approach the peak of the hurricane season. 


&& 


Aviation...expect prevailing VFR conditions across the local 
islands and at most taf sites tonight. However...MVFR or even brief 
IFR conditions and local mountain obscurations are still possible 
through about 23z in lingering showers and isolated thunderstorms. 


&& 


Marine...moderate period east-northeast swell being generated by Hanna will 
affect the regional waters over the next 36 to 48 hours...with the 
peak likely on Friday afternoon at about 3 feet along the Atlantic 
coasts of the local islands. Winds will be varying quickly as the 
circulation of Hanna passes the area during this time...with high 
pressure and moderate east-southeast to southeast flow expected over the weekend. 
Sea you in the water. 


&& 


Preliminary point temps/pops... 
sju 78 89 78 93 / 50 50 40 30 
stt 79 88 79 88 / 50 50 40 30 


&& 


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


$$ 


06/70/