Area Forecast Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14
000
FXPQ60 PGUM 282103
AFDPQ

Area Forecast Discussion
National Weather Service Tiyan GU
700 AM ChST Fri Jul 29 2016

.Synopsis...
Radar shows isolated showers and thunderstorms across the
Marianas waters. Gentle trades and 2-3 ft seas are also present.

&&

.Discussion...
Little change has been made to the forecast, as models still show
some mid-level drying today and tonight, then returning moisture
with a weak trough for the weekend with isolated thunderstorms.
But around Monday the GFS and the ECMWF begin to part ways. The
ECMWF takes an area of disturbed weather currently just NW of Wake
Island and develops it rather aggressively into a broad monsoon
circulation NE of the Marianas on Tuesday, with a monsoon tail
developing into the Marianas, and winds reaching 30 kt near the
circulation center by Thursday night well NE of the Marianas. The
GFS also develops the Wake Island disturbance, but much more
weakly than the ECMWF, with winds not much over 10 kt, and much
less rainfall. For now, forecast confidence is fairly high through
Sunday night, as the models are in good agreement then. But
confidence is low starting Monday, both in winds and weather,
until the models converge on how the circulation will develop and
affect the Marianas.

&&

.Marine...
Only minor adjustments were made to the marine grids. WW3 is
starting to show a small WSW swell coming in Sunday night and
Monday, most likely from the disturbance 96W east of the
Philippines. Have not incorporated it into the forecast yet;
waiting to see how 96W develops.

&&

.Eastern Micronesia...
A few weak trade-wind disturbances can be seen across Chuuk, Pohnpei
and Kosrae this morning. Farther east, a low-level convergent
boundary can be seen between 5N and 9N stretching east-northeastward
from near Majuro at 170E thru the Date Line to beyond 165W. At the
upper levels, a trough curves east-northeastward from a low centered
near Chuuk at 9N141E thru another low centered near Kwajalein at
10N169E to beyond 180 at 20N. The first upper low and related
trough will continue to interact with the disturbances to trigger
periodic showers and thunderstorms near Kosrae thru tonight, and for
Pohnpei and Chuuk thru Saturday. Divergent flow southwest of the
second upper low should maintain heavier showers and isolated
thunderstorms near the convergent boundary over Majuro thru this
evening.

As the convergent boundary pushes farther westward this weekend,
these heavier showers and isolated thunderstorms should also reach
Kosrae on Saturday, Pohnpei by Saturday evening and possibly Chuuk
on Sunday. By early next week, the upper-level features across the
region are expected to weaken. In conjunction with decreased low-
level convergence in the wake of the convergent boundary, drier
weather is going to spread from east to west.

&&

.Western Micronesia...
The Chuuk forecast discussion is included in the Eastern Micronesia
discussion above. Latest ASCAT/RapidSCAT composite imagery reveals
a surface trough extending southeastward from a tropical disturbance
centered northwest of Koror at 13N129E, passing between Koror and
Yap at 9N137E to end well south of Yap at EQ140E. Despite widespread
convection being suggested by model guidance, surface divergent
flow south of the trough axis near Koror has allowed showers to
decrease overnight. This phenomenon should continue near Koror thru
this evening. For Yap, modestly convergent winds north of the trough
axis will keep widely scattered showers there today. As the tropical
disturbance and associated trough pull farther northwestward tonight
and Saturday, a surface ridge near 142E will build westward and
bring fair weather over both locations. Unstable conditions will
return early next week as a series of weak trade-wind disturbances
arrives from the east.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...None.
Marianas Waters...None.

&&

$$

Middlebrooke/Chan



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.