Area Forecast Discussion
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FXPQ60 PGUM 300608

Area Forecast Discussion
National Weather Service Tiyan GU
408 PM CHST MON MAY 30 2016

A surface ridge remains over the Marianas and extends from SW to NE.
Light southeast winds have persisted for much of the day and have
been light enough to allow some heavy showers to develop along the
western coastline of Guam and just offshore. Infrared satellite and
PGUA radar echo tops show that some of the clouds reached up to near
25000 feet...but mid-level dryness limited thunderstorms from
developing. Higher up, an upper- level trough extends from SW to NE
over the region. Seas remain fairly flat...hovering between 2 and 3
feet, but the Ipan and Saipan buoys show that sea surface
temperatures have increased up to near 86 degrees after the past few
days of near- calm seas and light winds.


Little change was made in the short term forecast. The overall
pattern remains unchanged the next couple weeks. Model guidance is
in full agreement keeping the ridge axis right over the Marianas for
the next 10 days which will keep our surface winds weak, the daytime
feeling quite hot, and nights rather stagnant. Winds were just light
enough midday today to trigger some heavy showers from daytime
heating but there was too much mid-level dryness for thunderstorms
to really kick off. With model cross sections showing even drier air
aloft...decided to keep any chance of thunderstorms out of the
forecast for the next couple of days. However, with light southeast
winds, the western edge of Guam could see showers developing from
midday to late afternoon.

For the longer term forecast, a slight chance of thunderstorms
was included starting Friday. Island convection may be a contender
again as atmospheric moisture increases and low-level winds
remain light. Another wildcard comes into play with the upper-
level trough. Both GFS and ECMWF show an upper-level circulation
within the trough passing directly over the Marianas from the
east. The position of the upper-level low will be critical for the
potential for thunderstorms. At this point there`s still some
uncertainty exactly where it will pass but with it in the area, it
may spark off some thunderstorms.


.Eastern Micronesia...
Visible satellite imagery shows showery weather associated with a
convergence zone stretching from Kosrae to Majuro and to the date
line. Drier weather is seen to the west at Pohnpei and Chuuk. Latest
forecast reduces scattered showers at Kosrae and Majuro to isolated
as the bulk of showers are west Kosrae and east of Majuro. This
broad area of convergence will shift west maintaining showery
weather at Majuro and Kosrae through Tuesday night...and bringing
similar weather to Pohnpei and Chuuk Tuesday and Wednesday. Another
disturbance will bring another round of showers by the end of the
week to Majuro and Kosrae. Gentle to moderate trade winds are
expected through the week.


.Western Micronesia...
Reasoning for the Chuuk forecast can be found under the Eastern
Micronesia section above.

A surface ridge will maintain dry weather and gentle winds over
Koror and Yap thru Tuesday. The only exception will be the
possibility of afternoon thunderstorms near Koror due to island
heating. A surface trough merging into the ridge might trigger a few
showers for both places Tuesday and Wednesday. Afterward, the ridge
should rebuild over the area and provide drier weather into the


.GUM Watches/Warnings/Advisories...
Marianas Waters...None.


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