Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service tiyan GU
711 PM chst Tuesday Jul 28 2015
Updated to add micronesian discussion sections
latest pgua WSR-88D shows isolated showers over the marianas.
Light and variable winds prevail across the region.
no major changes to overall forecast. Updated wind grids for days
1 through 5 though no major differences were noted. A light wind
pattern is expected to continue through the next few days. Light
winds allowed island showers to develop across Guam...mainly over
the southern mountains...early this afternoon. This same scenario
is likely to repeat again on Wednesday as all conditions look to
be the same. Otherwise...a fairly benign pattern is on tap through
latest ascat showed a weak circulation centered south of Majuro.
The circulation is embedded within the monsoon trough that
passes north of Chuuk...Pohnpei and Kosrae...then south of
Majuro. Convergent monsoonal flow is generating a band of
convection that passes south of Pohnpei and Kosrae. Model guidance
keeps the bulk of the convection south of Pohnpei and Kosrae for
the next few days...but a slight shift of the band of convection
to the north would call for increased shower coverage in the
Pohnpei and Kosrae forecasts. Weak circulation near Majuro is
still expected to head west-northwest during the next several
days...passing to the north of Kosrae and Pohnpei. Quiet weather
pattern for Majuro appears to be setting up with no significant
weather makers on the horizon.
Wave watch model continues to show a 3 to 4 foot southern
hemisphere swell from the southeast to south-southeast arriving on
Chuuk...Pohnpei and Kosrae. Latest altimetry verifies the swell.
Swell will persist the next several days...but surf is expected to
remain below advisory levels. Surf will build on west-facing
reefs for these locations by the end of the week as upstream west
Chuuk discussion is included with the eastern micronesian
discussion due to a similar synoptic pattern.
Little change made to the Yap and Koror forecasts through the end
of the week. Did increase thunderstorm chances in the Koror
forecast for tonight based on 00z Koror sounding. Light to
moderate westerly monsoon flow and isolated showers should persist
the next several days. The area of showers and thunderstorms south
of Yap is beginning to encroach on Koror...but will maintain
current dry bias in the Koror forecast as best low-level
convergence should remain in the stronger monsoonal flow to the
south and east.