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Several tropical waves will appear during the upcoming week. one is
presently near 47 west and is expected to travel south of the area
on tuesday. models show a second becoming noticeable at 50 west on
sunday evening ... it is forecast to move into the area thursday night
and friday. this wave develops into a low pressure system south of
the dominican republic on the following weekend. a third wave is
shown near 42 west south of 10 north also on sunday evening. it
spins up into a depression that crosses 50 west at 15 north on
wednesday evening and reaches the lesser antilles 24 october.
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. Discussion ... Models show many strong features affecting the area
during the next 10 days. the high pressure to our north has already
lowered the precipitable water by more than one half inch and
drastically reduced convection across the entire forecast area. dry
air continues to feed into the area from the high through monday and
tuesday. although there appears to be some divergence aloft from the
approach of the shortwave aloft ... the dry air appears to squelch
most shower activity. the approach of a second stronger shortwave at
upper levels wednesday introduces strong flow from the southwest and
scattered areas of weak divergence aloft. that coupled with the
return of easterly flow will usher in the beginning of better shower
activity. then on thursday moisture from south america is picked up
on good southerly flow at both upper and mid levels and the wave
that approaches the area enhances the low level moisture. this would
portend a dramatic increase in shower activity with some possibility
of local flooding if all these elements come together as forecast.
since low pressure forms west of the area we are in the northeast
and most favored quadrant for good convection. the gfs shows the low
remaining in the vicinity of the dominican republic through sunday
with continued very moist low level southerly flow over puerto rico
and the u. s. virgin islands friday through sunday. such continued
flow can only bring large quantities rain to the area ... again if the
gfs has a reasonable handle on the situation. I dont know if this is what JB is talking about but it is interesting what the San Juan AFD says about the next 10 days.Let's see if apart from the GFS other global models show similar solutions.
