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Area forecast discussion 
National Weather Service San Juan PR
1042 am AST Wednesday Jul 30 2014 changes to previous...a few isolated showers beginning to expected through the afternoon.

&& changes...VFR conditions today at all taf sites xcpt
at jbq where a thunderstorms and rain is possible between 18z-21z. Winds mainly southeast
10-15 knots.


Previous discussion... /issued 544 am AST Wednesday Jul 30 2014/

Synopsis...surface high pressure across the west central Atlantic
is still expected to retreat north and into the northern Atlantic
by Thursday morning...leaving a surface low across the central
Atlantic and relaxing the pressure gradient while the local area
stays under an east southeast trade wind flow. Showers and
thunderstorm development expected today and Thursday mainly across
the northwestern quadrant of PR...with some but not much rainfall
expected elsewhere for the next few days. A TUTT low north of the
region and a weakly induced low level trough will shift further
north and west of the northeastern Caribbean through the latter
part of the week. An area of low pressure and associated tropical
wave near 44 west is forecast to further develop over the next few
days and reach the Lesser Antilles by the end of the work week.

Discussion...a patch of drier air is expected to move in today
across the local area. However there is still enough moisture to
cause showers and thunderstorms across the northwestern quadrant
of PR in the afternoon hours. The TUTT low is expected to remain
to the north of the islands causing some instability aloft. Since
the pressure gradient is expected to loosen quite a bit on
Thursday...the shower and thunderstorms that do develop are
expected to move slowly and also give the eastern interior
sections of PR a slightly higher chance of showers on Thursday
afternoon. Weak surface induced trough is expected to pass over
the area on Friday...this will increase available moisture even
more and once again help with the development od showers and
thunderstorms across the northwestern sections of PR while eastern
PR may observe scattered showers.

An area of low pressure now located around longitude 44 west
looks like it has limited shower and thunderstorm activity but it
does seem to be well organized. The National Hurricane Center
gives it a 70 percent of it developing into a tropical cyclone
within the next 48 hours. The expected impacts over the weekend
for the local islands are still uncertain. However at this
time...model guidance seem to agree a bit more with one another and has
this system passing very close to the northern USVI. This scenario
would give northeastern PR and the northern USVI some much needed
rain. However...confidence is low in this forecast as we are still
unsure of when will cyclogenesis will occur and how it will evolve
over the next several days.

Aviation...VFR conditions today at all taf sites xcpt at jbq where
a thunderstorms and rain is possible between 18z-21z. Winds mainly southeast 10-15 knots xcpt
westerly at jmz around 10 knots. Low pressure over the central Atlantic likely to
become td#3 tonight or Thursday and pass over the Leeward Islands Sat
afternoon and near or to the NE of the USVI late Sat night with IFR
conditions likely in heavy showers and T-storms over leeward and USVI

Marine...seas up to 4 feet and winds up to 17 knots are expected
over the coastal waters today.


Preliminary point temps/pops...
sju 89 77 88 77 / 10 10 20 30
stt 89 78 89 78 / 20 20 20 30


Sju watches/warnings/advisories...
Coastal waters...none.



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