Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 282023
Area Forecast Discussion
National Weather Service Tiyan GU
553 AM ChST Sat Oct 29 2016
Andersen Air Force Base Doppler weather radar shows isolated
showers moving through the Marianas waters. The VAD wind profile
reveals east-northeast winds of 10 to 20 knots through the lowest
15 thousand feet of the air. Above this the winds turn to the east
and increase a bit to between 15 and 25 knots.
Low confidence forecast today. Model agreement is fairly good as
is run-to-run consistency which would normally produce a higher
confidence forecast. However the trough we are expecting to come
through around Monday hasn`t started moving yet. The wind speeds
would also have to increase quite a bit over the next 48 hours.
All of this is possible, yet all the ifs are reducing our
After the disturbance goes by, conditions will dry out and winds
and waves decrease. The main uncertainty here is timing, as the
disturbance cannot go by until it arrives, and it cannot arrive
until it starts moving. Stay tuned...
Current forecast is based on slightly watered down model trends.
Winds of 20 to 25 knots and seas of up to 13 feet on Monday will
make marine conditions treacherous. Sailing on Monday is highly
discouraged, wait until Tuesday if at all possible.
The northeastern portion of a near-equatorial trough and embedded
weak circulations persist across Micronesia from near Chuuk east-
northeastward to the northern Marshall Islands. Convergent surface
winds near these features will maintain wet weather over Chuuk thru
tonight. On the other hand, surface ridging south of these features
will prolong fair conditions near Pohnpei thru Monday, Kosrae thru
Sunday night and Majuro until Sunday afternoon. As the trough and
associated circulations finally start to lift west-northwestward on
Sunday, this same ridging pattern should also build westward and
promote fair weather for Chuuk by Monday. Latest ASCAT and IR
satellite imagery indicates a trade-wind convergence zone forming
along 6N from the Date Line eastward to 160W. This zone might be the
next weather maker for Majuro and Kosrae early next week, Pohnpei
and Chuuk by midweek next week.
Reasoning for the Chuuk forecast can be found under the Eastern
Micronesia section above.
A near-equatorial trough has formed from the South China Sea,
extending eastward across Mindanao to a broad circulation centered
southeast of Yap near 5N144E. Meanwhile an upper-level trough is
also persisting near 13N north of Koror and Yap. Divergent winds
south of this upper trough will continue to trigger periodic
convection in the vicinity of the near-equatorial trough near Yap
thru Sunday night. For Koror, residual mid-level dry air should
hinder widespread convection until late tonight. However, island
heating might contribute a few thunderstorms this afternoon.
Conditions for both Koror and Yap next week will depend heavily on
the future development of the near-equatorial trough. Models are
still suggesting this trough will acquire monsoonal characteristics
and introduce convergent west to southwest winds by Tuesday. Future
shifts will need to amend the long-term forecast accordingly.