987
FXPQ50 PGUM 122056
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
656 AM ChST Fri Sep 13 2024

.Marianas Update...
Tropical Storm Bebinca is having trouble maintaining its convection,
which is having a ripple effect back down the monsoon band feeding
into it. The weakened band is being pushed westward by a ridge,
allowing much improved weather today. For now the band is expected to
come back tonight, this will be reevaluated as the day goes on.
Otherwise no changes were made to the forecast.

&&

.Marine...
Seas of 8 to 10 feet will continue to gradually diminish. The Small
Craft Advisory is on schedule to expire this evening at 6 PM. Winds
are already under criteria, and seas will be this evening.

&&

.Hydrology...
Convection has really dried up the last few hours, so the forecast
today had the showers reduced dramatically. Will maintain the flood
watch for now as the showers could come back tonight. If it looks
like they won`t, the flood watch will likely be canceled at that
time.

&&

.Tropical systems...
Tropical Storm Bebinca is currently near 21.7N and 138.4E. It is
having trouble maintaining its convection right now, probably because
an upper-level low has formed too close to it toward the west. This
is creating a ripple effect in the monsoon band that was feeding it.
It`s uncertain if the band will ultimately weaken itself, move to
feed another target, or if Bebinca will recover.

&&

.Eastern Micronesia...
Little change to the forecast. Recent Himawari satellite imagery
showed scattered showers developing over Pohnpei this morning, with
fairly clear conditions to the southeast over Kosrae. Expecting
scattered showers to continue within the messy region of convergence
and troughing located near Pohnpei, with areas of numerous showers to
develop at times today. Models indicate these showers to move
northwest and away from Pohnpei overnight, yielding quiet conditions
for the weekend. Late Sunday, an ITCZ disturbance will push west from
over the Marshall Islands, bringing showers to Kosrae Sunday night
and then Pohnpei during the early week.

Majuro sits just south of a trough embedded within the ITCZ, and
satellite shows scattered showers and isolated thunderstorms to
Majuro`s north and southeast. Majuro will remain in the vicinity of
an intermittently-active ITCZ, and can expect scattered showers and
isolated thunderstorms this weekend and for much of next week.

No major updates to the marine forecast. Seas remain between 4 and 6
feet across eastern Micronesia, and no marine hazards are currently
anticipated.

&&

.Western Micronesia...
A High Surf Advisory, Small Craft Advisory, and a Special Weather
Statement remain in effect for Yap and Palau.

No major changes to the forecast as Palau and Yap continue to see
effects from the monsoon surge over far western Micronesia. Although
there is a general drying trend across the region, latest satellite
imagery shows scattered showers developing in the vicinity of Palau,
and numerous showers are located within the northeast-to-south
periphery of Yap. Overnight scatterometry showed areas of 20 to 30 kt
southwesterly winds east of Palau and over Yap. Surface observations
at Palau continue to show fresh to strong southwest winds with
occasional near-gale gusts. The High Surf Advisory and Small Craft
Advisory remain in effect until Saturday evening, but Small Craft
conditions may continue into early next week for Yap as TS Bebinca
tracks northwest over the Philippine Sea.

No changes to the marine forecast. Recent satellite altimetry shows 9
to 13 ft seas directly east of Yap as fresh to strong monsoon winds
continue near Yap and Palau. Chuuk is expect to see a continuation
of 4 to 6 ft seas, with gentle to occasionally moderate winds
anticipated to persist into next week.

&&

.Prev discussion... /issued 454 PM ChST Thu Sep 12 2024/

Marianas Synopsis...
Satellite and radar observations show continued influences from the
monsoon surge that is tailing Tropical Storm Bebinca. Numerous to
widespread showers are seen across the Marianas. Combined seas range
between 9 and 12 feet.

Discussion...
Overall, there isn`t much change in thinking on the forecast since
yesterday. The ECMWF has shifted slightly towards the rest of
consensus for the Sunday night through Tuesday time period. As such,
the forecast trended towards slightly stronger winds. There will be a
brief break in the windy conditions on Saturday and much of Sunday
before the monsoonal surge re-intensifies. Heavy rain is expected to
continue through Monday and the Flood Watch will likely need to be
extended with upcoming forecasts. Please see the hydrology section
for more details. Those in the Marianas should continue to monitor
forecasts for changes towards the early week period. Towards the
middle of next week, signs point to quieter conditions filtering into
the region.

Marine...
The Small Craft Advisory has been extended until 6 PM Friday evening
for the Marianas Coastal Waters. Combined seas of 9 to 12 feet will
persist through Friday afternoon as the monsoonal flow continues. The
High Surf Advisory was continued for south facing reefs and started
for west facing reefs. The High Surf Advisory will continue until 7
PM Saturday evening. Seas are expected to subside some on Saturday
night before quickly increasing back to hazardous conditions on
Sunday or Sunday night. The High Surf Advisory may need to be
extended into Sunday if seas are slower to subside than expected.

Hydrology...
The Flash Flood Watch continues until Saturday morning for the
Marianas. 7 to 11 inches of rain have already fallen the last couple
of days and an additional 3 to 5 inches of rain will be possible
during the watch period. Heavy rain is likely to continue into the
weekend and the Flash Flood Watch will likely need to be extended
barring sudden shifts in the monsoonal flow.

Localized flooding will be possible in low-lying and poor drainage
areas, while flash flooding could also be possible in areas of
heaviest rainfall. This situation will continue to be monitored
closely and additional Flash Flood Warnings may be issued if
conditions warrant.

Tropical systems...
An asymmetric TS Bebinca continues to pull away from the Marianas.
Recent scatterometer passes show the asymmetric wind field with the
strongest winds all to the north and east of the storm and much
weaker winds to the southwest. Bebinca will have no direct effects on
the Marianas, but, indirectly, could eventually push some NW swell
into the region as it continues to grow and intensify.

Directly affecting the region is the broad southwesterly monsoon tail
flowing up into Bebinca. It is maintaining hazardous marine and
weather conditions across far western Micronesia and across the
Marianas where wind gusts as high as 50 mph (at the Saipan Airport) are
still being reported. The wet and blustery weather will persist the
next day or two before lifting northward. However, computer models
still hint at a disturbance, or pair of disturbances, taking shape
near and east of the Marianas that would lead to an eastward
expansion and strengthening of the monsoon flow in the area. Whether
any additional TCs form in this region or not is still widely
uncertain with models showing a lot of run-to-run variability.

Eastern Micronesia...
Quiet conditions are seen at Kosrae and Majuro, but Pohnpei remains
in the midst of showers and thunderstorms associated with a
westward-drifting surface trough. This trough will stall near Pohnpei
the next couple of days, prolonging wet conditions through at least
Friday. The broader monsoon pattern across West Micronesia and the
Marianas is largely dominating regional weather and the subtropical
ridge has also been pushed to the north of 30N. This has ultimately
weakened the easterly flow across East Micronesia. Over the next few
days, weak disturbances between Wake Island and the Marianas,
including a large upper-level low enhanced convective flare up west
of Wake Island, will fully break down the surface wind pattern with
much of the region west of 165E seeing winds 5 mph or less. South of
10N, a shallow low-level ridge should set up over the weekend across
Pohnpei and Kosrae. By Sunday, a westward-moving surface trough will
move through the Marshalls and progress toward Kosrae and Pohnpei by
Monday.

Seas remain between 5 and 6 feet across the region and little change
is expected the next few days. Over the weekend, a small west swell
will enter the region from the strong westerly winds now found near
Yap and Palau. No marine hazards are currently anticipated.

Western Micronesia...
A High Surf Advisory, Small Craft Advisory, and a Special Weather
Statement remain in effect for Yap and Palau.

Little change to the forecast. Latest satellite imagery shows
numerous to widespread showers over Yap and Palau, which are in the
midst of a monsoon surge flowing into Tropical Storm Bebinca, located
about 600 nautical miles north of Yap. Over the day, METAR
observations at Palau have shown southwest to west winds sustaining
in the 15 to 25 kt range with higher gusts of near gale force at
times. The High Surf Advisory and Small Craft Advisory remain in
effect until Saturday evening, but Small Craft conditions may
continue into early next week for Yap as TS Bebinca tracks northwest
over the Philippine Sea. The surge is anticipated to linger through
the remainder of the week and begin to diminish this weekend for
Palau, and later for Yap. Palau may come out of the monsoon early as
the monsoon flexes northward with TS Bebinca. Ensembles show a
possibility for additional rainfall totals of 6 to 8 inches over the
next few days, increasing the risk of mudslides in Palau.

Chuuk can expect to see scattered showers this week due to normal
wet season trade-wind troughs pushing through, and should taper off
to isolated for the weekend.

Satellite altimetry reveals combined seas of around 5 to 6 feet between
Yap and Chuuk. As the monsoon surge progresses, seas are anticipated
to reach 9 to 13 feet near Yap and Palau, with fresh to strong winds
gusting to gale force occasionally. Chuuk is expected to be much
more relaxed, with combined seas of 4 to 6 ft expected to continue.
Winds near Chuuk are anticipated to remain gentle to moderate for the
remainder of the week.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...Flood Watch through Saturday morning for GUZ001.

     High Surf Advisory until 7 PM ChST Saturday for GUZ001.

MP...Flood Watch through Saturday morning for MPZ001>003.

 High Surf Advisory until 7 PM ChST Saturday for MPZ001>003.

Marianas Waters...Small Craft Advisory until 6 PM ChST this evening
                  for PMZ151>154.

&&

$$

Marianas: Stanko
Micronesia: DeCou