Area Forecast Discussion
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FXPQ60 PGUM 250811

Area Forecast Discussion
National Weather Service Tiyan GU
611 PM CHST WED MAY 25 2016

A surface ridge anchors from north of Wake Island southwestward
across the Mariana Islands to near Mindanao in the southern
Philippines. A stationary front remains to the north near 11N and
a trade-wind convergence zone persists to the southeast across
eastern Micronesia. A weak trade-wind disturbance is departing the
Marianas this evening.


A few passing showers associated with the departing disturbance
should end by midnight then follow by an area of dry air thru
Thursday afternoon. Three more weak disturbances are upstream near
150E, 155E and 168E. They will follow a similar path and merge
into the ridge while passing thru the Marianas. Based on the
latest sounding data this afternoon, there is modest increase in
moisture up to 550mb. This will be enough to trigger periods of
isolated showers from Thursday evening to Sunday.

Visible satellite loop and ASCAT image reveal a monsoon
circulation has developed southeast of Hainan Island near 17N113E
in the South China Sea. Moderate to fresh convergent west to
southwest monsoon winds are now just west of the Philippines. A
surface trough extends east-northeastward from the monsoon
circulation thru Taiwan to near Iwo To Island. The GFS model suite
still suggest the ridge across the Philippine Sea will weaken
enough to allow monsoonal southwest winds over the South China Sea
to push eastward into the Philippine Sea and reach the Marianas
next week. Still flavored in the ECMWF and NAVGEM on keeping the
ridge in place next week. Therefore, gentle trade-wind swell and
benign sea conditions will prevail into next week.


.Fire weather...
Isolated showers from now thru Sunday will offer little relief on
the already very dry fuels across Guam. However, red flag
conditions are not expected as trade winds will remain gentle to


.Eastern Micronesia...
Satellite imagery this afternoon shows a partial ITCZ stretching
from just west of Chuuk, through Pohnpei and Kosrae to just south
of Majuro. This area is also being aided by the development of a
Tropical Upper Tropospheric Trough (TUTT) to the north of 10N
which is providing some nice westerly divergence. Both the GFS and
ECMWF show this scenario but perhaps the ECMWF depicts the
moisture field a little more clearly. Other than westerly moving
impulses in the trade wind flow...there are no significant
features that can be pinpointed for specific-day forecasts. In
general, expect Pohnpei to let up a little on Thursday while
Kosrae will stay active for another day or two. The ECMWF pushes
the ITCZ back over Majuro by late Thursday, providing more much
needed rainfall. Sea conditions show mostly a moderate trade-wind
swell through out, which puts Kosrae just below the 8ft high surf
conditions for east facing reefs tonight. These conditions should
subside after tonight.


.Western Micronesia...
Some rather significant changes have occurred for Koror and Yap
today with most showers having pushed well to the west and north
of these islands, leaving practically clear skies and very nice
ridge-like weather. Models are not particularly useful with
this...and so this forecast brings back the clouds and showers by
the weekend but with no particularly interesting feature to hang
ones hat on. The weak ridge to the north seems to be the cause of
the weather but it is doubtful it will last too long with the
southeast monsoon now developing just to the west of the
Philippines in the South China Sea. Little change in the Chuuk
forecast on this run. Perhaps a temporary reprieve for the next
day or two, before the activity just to the east pushes in.


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


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