373
FXPQ50 PGUM 182004
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
604 AM ChST Thu Sep 19 2024

.Marianas Update...
A weak trough and an upper-level low are combining to bring scattered
showers and isolated thunderstorms to the Marianas today. Overnight
the showers should diminish to isolated. Combined seas have dropped
to 4 to 6 feet, and could reach 3 to 5 feet over the weekend. A
moderate risk of rip currents along east and west reefs could become
low along all reefs at some point. Overall little change in the
forecast, everything looked to be in good shape.

&&

.Eastern Micronesia...
A couple of troughs at the leading edge of the ITCZ, one is building
into Kosrae and the other is approaching Majuro. Patchy convection
is associated with this overall pattern, although deepening
convection and some lightning are observed farther east, closer to
the Date Line. Latest model guidance still shows moderate development
of the ITCZ through Saturday, so the forecast remains on track, with
scattered showers building into Kosrae and Majuro today and for
Pohnpei tonight. The peak in showers is expected Friday and
Saturday, then the ITCZ dissipates once again bringing fairer
conditions for all forecast locations Sunday into early next week.

&&

.Western Micronesia...
Overnight scatterometry reveals gentle to moderate winds over Yap and
Palau associated with a weak ridge between the monsoon and trade
patterns. Satellite imagery and the GLDN shows the thunderstorms
near Palau have shifted farther south overnight and spotty showers
and thunderstorms are developing across eastern Yap State and western
Chuuk State from multiple trade-wind troughs and favorable upper-
level support. Calmer conditions are seen over Yap and Palau
currently, so lowered POPs for today. Expect off-and-on showers
through the weekend with weak troughing and convergence in the trade
pattern. No changes needed for Chuuk, isolated showers expected
through tonight, then ITCZ showers build in Friday and Friday night.

&&

.Prev discussion... /issued 550 PM ChST Wed Sep 18 2024/

Marianas Synopsis...
Satellite imagery shows the cloud cover this morning is starting to
break up, but more showers and thunderstorms are developing to the
east of the coastal waters. The airports across the Marianas are
reporting are reporting light to gentle winds, while combined seas
are 5 to 7 feet according to latest buoy and altimetry data.

Discussion...
An approaching Tropical Upper Tropospheric Trough (TUTT) and
associated upper-level low will increase instability over the
Marianas, helping to support the development of showers and
thunderstorms along any weak troughs passing through. This will keep
the risk for periods of scattered showers and isolated thunderstorms
in the forecast through Thursday night. For Friday and Saturday, TUTT
is expected be well northwest of the Marianas, allowing cloud cover
and the potential for showers and thunderstorms to decrease.
Potential for showers will start to increase again Sunday and Monday
as models shows the next series of troughs moving in from the east.

Marine...
Mainly gentle trades will are expected through the weekend. The
southwest to west swell will continue to decrease through the week
allowing seas around 5 to 7 feet, to drop to 4 to 6 feet by Friday,
and maybe 3 to 5 feet early next week. The decreasing swell will
also allow surf to slowly drop along west facing reefs. Weak troughs
and an approaching TUTT will keep scattered showers and isolated
thunderstorms going at times through Thursday night, with the
potential for showers and thunderstorms decreasing for Friday and
Saturday.

Tropical systems...
Pulasan (15W) briefly became a typhoon earlier today but has since
weakened back down to a tropical storm. Tropical Storm Pulasan is
located near 24N130E this evening, just on the edge of WFO Guam`s
area of responsibility and is expected to exit the region over the
next few hours. Once Pulasan exits the region, tropical cyclone
activity is not expected through the weekend and into early next
week.

Eastern Micronesia...
A dry pattern is currently in place across Kosrae and Pohnpei, with
wetter conditions seen across Majuro. A weak, but developing, ITCZ
(Inter-tropical Convergence Zone) is seen over the Marshalls,
stretching southeast from near Enewetak to southeast of Majuro.
Scattered showers and isolated thunderstorms look to continue across
Majuro as the ITCZ slowly meanders around the region. Majuro should
see a drier pattern later this evening that will be fairly short-
lived, as a trade-wind trough approaches from just east of the Date
Line and interacts with the tail of the ITCZ, bringing increased
showers back to the atoll for Thursday. There are a couple more
troughs east of the Date Line that will move into the Marshalls by
the end of the week. The ITCZ should also be a bit more developed by
then. This should bring numerous/likely showers and a few
thunderstorms to the atoll into Saturday. Convection should begin to
wind down Saturday afternoon or evening, followed by a drier pattern.
For Kosrae, a more moist pattern will move in by Thursday morning as
the aforementioned ITCZ approaches. Along with the ITCZ, the series
of troughs moving through the Marshalls look to interact with the
ITCZ, resulting in increased convection there as well. However, POPs
look to remain a bit lower for Kosrae. Farther west, Pohnpei will see
similar conditions as Kosrae, though this will occur about 12 hours
later than Kosrae. Over the weekend, all three locations will see
drier conditions that could last through the middle of next week.

Benign marine conditions look to continue through the next several
days, with combined seas of 3 to 4 feet at Pohnpei and Kosrae, while
seas could reach as high as 5 feet for Majuro. Light to gentle winds
are expected through the beginning of next week.

Western Micronesia...
Satellite trends this afternoon show a gradual clearing of heavy
showers and thunderstorms near Palau and Yap as ridging builds over
the area behind the weakening monsoon trough, which is shifting
further northwest with the movement of TS Pulasan. Still, areas of
thunderstorm development are seen to the southeast and just west of
Palau, maintained by low-level convergence within the southeasterly
flow and strong divergence aloft. POPs were bumped up slightly for
tonight given persistent convection and scattered showers across the
area. Weak troughing and convergence in the easterly trades will keep
scattered showers in the forecast over the next few days, with
increasingly spotty coverage heading into the weekend. By early next
week, a broad ridge will set up over far western Micronesia, leading
to a drier pattern for the first half of next week.

Farther to the east, satellite shows scattered to numerous showers
developing to the north of Chuuk State along the axis of a broad
trade wind trough. Thick upper-level cloud debris from these showers
blankets the skies over Chuuk, but showers are isolated across the
local area. Little change was made to Chuuk`s forecast. Isolated to
scattered showers are expected for the next few days until a trough
at the leading edge of the ITCZ increases showers come Friday.

Little change needed for the marine forecast. The Babeldaob buoy off
Palau`s east coast is showing 2 to 4 ft seas as it captures a south-
southeast swell, which is expected to become a 3 ft east swell by
the weekend. 3 to 5 ft seas near Chuuk will come down another foot or
so by next week as winds become light to gentle.

&&

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

$$

Marianas: Stanko
Micronesia: Cruz