631
FXPQ50 PGUM 150808
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
608 PM ChST Mon Jul 15 2024

.Marianas Synopsis...
Trade winds and isolated showers are seen across the Marianas waters.
Further east, showers and isolated thunderstorms are seen approaching
the waters. Marianas buoys are reporting 4 to 5 feet.

&&

.Discussion...
No major changes to the forecast. A few showers are seen near the
Marianas which is expected to pass through tonight with only isolated
showers. A gradual increase in shower potential is expected trending
from scattered to numerous showers Tuesday through Wednesday night as
the monsoon trough lifts north and interacts with a descending
Tropical Upper Tropospheric Trough (TUTT). Thursday through Sunday`s
forecast is the same as yesterday`s with a decreasing trend of
showers, but possible we may see slightly higher potential for
showers for the islands through the weekend, and higher gusts for
Saipan and Tinian on Thursday, based off of GFS. For now, keeping
closer to the ECMWF solution for the longer term.

.Marine...
Gentle to moderate trades are expected across the Marianas through
Friday, becoming fresh at times Tuesday night and with occasional
strong gusts starting Thursday. Seas of 4 to 5 feet today will become
5 to 7 feet by end of the week. A west swell is expected to start
building Tuesday evening as a result of the monsoon activity near
Palau.

&&

.Eastern Micronesia...
The Inter-Tropical Convergence Zone (ITCZ) remains fairly active
across the Marshall Islands and Kosrae, generating scattered to
numerous showers and isolated thunderstorms. Over by Pohnpei, most of
the shower and thunderstorm activity is north of Pohnpei as the
greatest convergence is associated with the trade-wind surge north
Pohnpei near 10N, but some scattered showers are still developing
around Pohnpei, and more showers and thunderstorms will move in from
Kosrae later tonight. As showers and thunderstorms near Kosrae and
Majuro continue to push westward, expect numerous, locally heavy
showers to develop across Kosrae and Pohnpei Tuesday, while showers
are expected to be more scattered in coverage across Majuro and the
northern Marshall Islands. The trade- wind surge however, will
strengthen over the Marshall islands later tonight and Tuesday,
bringing breezy conditions of 20 to 25 mph across the Marshall
Islands. Winds will then start to weaken Tuesday night. The ITCZ is
still expected to slowly fragment into a series of troughs later this
week as models show the ITCZ losing its southeast winds. This
pattern will still support showers and thunderstorms across the
region, with some being locally heavy showers possible, but showers
will start to cluster more around the troughs allowing for greater
variation in shower coverage from day to day.

Altimetry data shows seas are 4 to 5 feet around Pohnpei and Kosrae,
and pushing up to 6 to 8 feet around the Marshall Islands, where
winds are slightly stronger due to the trade-wind surge. As the
trade-wind surge rebuilds across the Marshalls tonight 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 kept the headline in the forecast for Majuro`s coastal waters to
highlight the potential for choppy seas tonight and Tuesday, with
winds then decreasing for the second half of the week. 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, extending across the Philippines, passes through
JTWC`s Invest 91W near 8N129E, and continues southeast, across the
main islands of Palau and south of Yap State, ending near EQ152E. The
region is divided between monsoon west-southwesterly flow, over
Palau, colliding with the trade-wind pattern across Yap and Chuuk.
Showers are slow to build back into the main islands of Palau, so
delayed the onset of numerous showers to late tonight. 91W is
diverting some of the monsoon flow, making it difficult for showers
to reach Palau lately. 91W is currently rated "low" for development
and will not have any impact to the region since it is off to the
west. Overall, a fairly active monsoon pattern will persist, creating
unsettled weather for the region. Model guidance shows a gradual
north to northwest shift of the monsoon trough, maintaining showery
monsoon weather in far western Micronesia, with locally heavy rain
and gusty winds possible for Palau and Yap through Wednesday night.
Between the monsoon and trade-wind patterns, a broad trough is
traversing Chuuk tonight and is generating widespread showers and a
few thunderstorms. Showery weather persists through the week with
the ITCZ pattern remaining across eastern and central Micronesia,
possibly fragmenting near Chuuk late week. Even so, trade-winds
troughs passing through the ITCZ are still expected to heighten
shower and thunderstorm activity at times.

Altimetry and scatterometry data show seas of 3 to 6 feet and light
to moderate winds. However, localized effects of heavier showers
will still lead to choppy seas across Palau and Yap over the next
few days. Southwest to west winds and swell in far western Micronesia
will further develop, allowing for seas to build up to 7 feet around
Wednesday or Thursday, especially for Palau, while seas near Chuuk
look to stay between 4 and 6 feet.

&&

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

$$

Marianas: Hong
Micronesia: Schank/Cruz