396
FXPQ50 PGUM 142035
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
635 AM ChST Mon Jul 15 2024

.Marianas Update...
Little change from the previous forecast. The thunderstorms of last
night have pushed off to the west, leaving the weather calm and
sedate through at least tonight. The next disturbance is expected to
approach Tuesday afternoon, and will increase showers back to
scattered coverage, and reintroduce isolated thunderstorms.

Seas are expected to remain around 4 to 6 feet in the latest run of
the ECMWFwave. This is a slight decrease from previous runs, which
had the seas increasing to between 5 and 7 feet. Due to this slight
nudge downward, surf could diminish to between 5 and 7 feet along
east facing reefs, but this is still a moderate risk of rip currents,
so the moderate risk looks likely to continue through the end of this
week and probably beyond. There is a small west swell expected to
arrive as a result of the monsoon activity near Palau. The main
effect of this will be to raise the surf for west facing reefs to
between 2 and 4 feet instead of around 1 foot.

&&

.Eastern Micronesia Update...
Satellite observations show scattered showers and thunderstorms near
Majuro and Pohnpei with showers and storms bending well north of
Kosrae. Latest Altimetry data shows seas of 5 to 8 feet near Majuro
and seas of 4 to 6 feet new Kosrae and Pohnpei.

Little change was made to the forecast. The Inter-Tropical
Convergence Zone (ITCZ) still remains active across eastern
Micronesia. Scattered showers should build into the region today and
tonight impacting Majuro, Kosrae, and Pohnpei. Models still hint
towards the ITCZ slowly fragmenting into multiple troughs later this
week. The trade- wind surge is still expected to bring winds of 20
to 25 mph to the Marshall Islands tonight and into Tuesday.

Seas will raise another foot or so across the Marshall Islands up to
9 feet within the coastal waters. Seas look to remain below small
craft advisory criteria, but kept the headline from the previous
forecast detailing the potential for breezy conditions and choppy
seas.

&&

.Western Micronesia Update...
Satellite observations show scattered thunderstorms across Yap State
while the lull in showers and storms remains over Palau. Altimetry
shows combined seas between 3 to 5 feet near Yap and 4 to 6 feet to
the west of Palau`s coastal waters.

The main change for this package was to Yap`s forecast for today and
this afternoon. Scattered showers and storms have already impacted
Yap early this morning and satellite shows further development to
the east of Yap. As a result, PoPs were increased to 50% during the
morning and 60% for this afternoon as coverage is expected to
increase through the day. Otherwise, little change from the previous
forecast. The lull across Palau should come to an end this morning
as the diffluent flow shifts westward. Scattered showers and isolated
storms should develop this morning and become numerous this
afternoon. Latest satellite trends show scattered showers developing
near Chuuk. Coverage is expected to become numerous overnight as the
ITCZ begins to stretch into the region.

Localized effects of heavier showers will lead to choppy seas across
Palau and Yap over the next few days. Southwest to west swell waves
and westerly surface winds will further develop, allowing for seas to
build to 4 to 7 feet over the next few days, especially for Palau.
Ngaraard, Babeldaob Buoy still shows seas around 2 to 3 feet, since
it is shielded from westerly waves. For Chuuk, gentle to moderate
trades with stronger gusts near showers and seas of 4 to 6 feet are
expected for the next several days.

&&

.Prev discussion... /issued 552 PM ChST Sun Jul 14 2024/

Marianas Synopsis...
Moderate trades and localized trade showers are seen across the
Marianas with seas 4 to 6 feet. Expect isolated showers and
thunderstorms through tonight.

Discussion...
Isolated thunderstorms were seen across the waters today and is
expected through tonight, and showers look pretty isolated east of
the waters. For Monday and Monday night, expecting a little more
subsidence, so forecasted isolated showers without thunderstorms.
From Tuesday through Thursday, the monsoon trough is seen extending
across from Koror and Yap, reaching into the Marianas. At the same
time, a Tropical Upper Tropospheric Trough (TUTT) moves into the
area. Both GFS and ECMWF indicate a possible circulation developing
near Yap Wednesday, but after that, solutions diverge as far as
development and direction of movement. Both models show a southeast
wind with showers developing around Tuesday night. Adjusted the
previous forecast slightly, scattered showers starting Tuesday night
and ending around Thursday. Still, Friday and Saturday forecasts are
a little more uncertain. If a tropical disturbance develops near Yap,
we may see higher potential for showers over the weekend. If not,
trades push through with less shower potential.

Marine...
Gentle to moderate trades are expected to continue for the Marianas
tonight and for next few days. Starting Tuesday night, expect an
increase in showers, winds and wind waves. Easterly swell heights
are expected to see little change, but a 2 to 3 foot swell should
develop near the end of the week as west-southwest winds associated
with the monsoon trough strengthen.

Eastern Micronesia...
The Inter-Tropical Convergence Zone (ITCZ) remains fairly active
across the region, generating scattered to numerous showers and
isolated thunderstorms from the Marshall Islands to Pohnpei this
evening. In the short term, satellite imagery shows weather clearing
to the east of Kosrae so expect showers to briefly become isolated at
Kosrae tonight, before increasing again Monday as the showers south
of Majuro push westward into Kosrae. The ITCZ is expected to slowly
fragment into a series of troughs later this week as models show the
ITCZ loosing its southeast winds. This pattern will still support
showers and thunderstorms across the region, with some being locally
heavy, but showers will start to cluster more around the troughs.
Another feature that has so far played a minor role is the trade-wind
surge north of the Marshall Islands. The trade-wind surge is
currently fragmented with pockets of winds around 20 to 25 mph mainly
north of the Marshall Islands and near the Date Line. However,
models show the trade surge rebuilding across the Marshalls Monday
night into Tuesday bringing breezy conditions of 20 to 25 mph to most
of the Marshall Islands, with winds then relaxing back to the 10 to
20 mph range later in the week.

Altimetry data shows seas are 3 to 5 feet around Pohnpei and Kosrae,
and pushing up to 6 to 7 feet north of the Marshall Islands, where
winds are slightly stronger due to the trade-wind surge. As the
trade-wind surge rebuilds across the Marshalls Monday night and
Tuesday, seas are expected to build up to 9 feet with sustained
winds around 20 knots. This is just below small craft conditions of
10 feet and/or winds of 22 knots or greater, so held off on an
advisory for Majuro, but added a headline in the forecast for
Majuro`s coastal waters to highlight the potential for choppy seas
Monday night and Tuesday. Otherwise seas are expected to build a foot
at Pohnpei and Kosrae over the next few days with some slightly
stronger winds near heavier showers and thunderstorms.

Western Micronesia...
The monsoon trough extends across the region, passing just north of
the main islands of Palau then continues southeast ending near
EQ152E. The region is divided between monsoon west-southwesterly
flow, over Palau, colliding with the trade-wind pattern set up over
Yap and Chuuk. An embedded disturbance is south of Eauripik in
eastern Yap State and is helping induce diffluent flow near and east
of Palau. A decrease in shower coverage is evident on satellite, so
trimmed back shower coverage in Palau`s forecast tonight and tomorrow
morning. However, this is a brief lull and locally heavy showers
with stronger gusts are still possible with the unsettled weather
pattern in the region. Models show the potential of a north to
northwest shift of the monsoon trough over the next few days,
bringing abundant showers and thunderstorms for Palau for most of the
week and for Yap starting Monday night or Tuesday, with heavy
downpours and gusty winds expected. For Chuuk, showery weather
persists through the week due to the ITCZ pattern stretching across
from eastern Micronesia, possibly fragmenting near Chuuk late week.
Trade-winds troughs passing through the ITCZ are expected to
heighten shower and thunderstorm activity at times.

Localized effects of heavier showers will lead to choppy seas across
Palau over the next few days and for Yap state in the coming days.
Southwest to west swell waves and westerly surface winds will further
develop, allowing for seas to build to 4 to 7 feet over the next few
days, especially for Palau. Ngaraard, Babeldaob Buoy still shows
seas around 3 feet, since it is shielded from westerly waves. For
Chuuk, gentle to moderate trades with stronger gusts near showers and
seas of 4 to 6 feet are expected for the next several days.

&&

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

$$

Marianas: Stanko
Micronesia: Williams