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AXPQ20 PGUM 140052
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1052 AM ChST Sun Jul 14 2024

Tropical Weather Discussion for the Western North Pacific between
the Equator and 25N from 130E to 180. The following information is
based on recent satellite imagery/data, weather observations, radar,
and meteorological analysis.

...SPECIAL FEATURES...

None.

...OTHER WEATHER SYSTEMS...

MONSOON TROUGH...
The monsoon trough, extending across the Philippines, enters western
Micronesia near 9N130E and then continues southeast, across the main
islands of Palau, and ends near EQ150E. Overnight scatterometer data
showed a couple of areas of sharped curvature within the trough,
southeast of Palau near 7N138E and well southwest of Chuuk near
3N147E. Morning visible satellite imagery at these two locations did
not show any discernible circulations near these locations, but the
monsoon pattern is known to give rise to short-lived vorticity
features that can quickly develop and then dissipate over a 12 to 24
hour period. Along and south of the trough, widespread locally heavy
showers and isolated thunderstorms are developing across western
Micronesia, especially across and around the main islands of Palau.
Yap Proper is north of the monsoon trough, but trade-wind flow into
the monsoon trough is producing spotty to scattered showers around
Yap.

The monsoon trough is expected to continue across western Micronesia
over the next couple of days supporting locally heavy showers and
thunderstorms, along with gusty westerly winds across Palau. Models
shows the potential of a north to northwest shift around mid-week, as
the monsoon trough follows disturbances that develop in or near the
trough. Over the next 7 days, the greatest potential for tropical
cyclone development will mainly be west of our region, in the far
western portions of the Philippine Seas and South China Sea.

TRADE-WIND SURGE...
The trade wind-surge has weaken slightly since yesterday, with
scatterometer data showing 15 kt winds between 7N and 25N, from 155E
to beyond the Date Line, extending back towards Hawaii. Pockets of
20 kt to 25 kt are seen near 170E and especially along 180 and areas
eastward. Low-level convergence is generating patchy showers in this
area, with some scattered showers and isolated thunderstorms across
the the northern Marshalls where the trade surge is interacting with
the ITCZ, discussed in more detail below. Models show this surge
rebuilding across the Marshall Islands around Monday potentially
bringing some choppy seas and winds near 22 kt to Majuro and
surrounding islands. The trade-wind surge will then weaken as the
surface high to the distant north continues to propagate eastward,
relaxing the pressure gradient in the region in the second half of
the week.

TUTT...
The TUTT extends across the region from northwest of Wake Island
near 30N160E, through an upper-level low near 24N156E, passing
through the northern Marianas Islands north of Saipan to a second
upper-level low west of the Marianas near 15N140E, and exiting the
region near 15N130E at it continues towards the Philippines.
Scattered showers and thunderstorms are developing along the TUTT,
especially around the two upper-level lows. Satellite imagery shows
some isolated cumulus towers that try to develop and then quickly
collapse across the Marianas, supported by the upper-level
divergence associated with the TUTT, so the Marianas may see some
isolated thunderstorms develop within the coastal waters this
afternoon. The TUTT is expected to drift westward over the next few
days, providing upper-level support over the monsoon trough in
western Micronesia, while the upper-level low northwest of Wake
Island is expected to move north of the Marianas around the middle of
the week, increasing the potential for thunderstorms across the
Marianas.

...ITCZ...
The ITCZ stretches across eastern and central Micronesia, passing
across the Date Line around 6N and meandering through the region,
passing near Majuro, Kosrae, Pohnpei and Chuuk, then meets the
monsoon trough as it pushes into eastern Yap State, around 6N142E.
Scattered to numerous showers and isolated thunderstorms are
developing along the ITCZ, especially between the equator and 8N,
with showers and thunderstorms developing up to 11N in the Marshall
Islands due to the trade-wind surge north of the Marshall Islands.
The ITCZ is expected to slowly fragment into a series of trough later
this week as models show the ITCZ loosing its southeast winds. This
pattern will still supported scattered showers and isolated
thunderstorms across the region, but showers will start to cluster
more around the troughs.

$$

Schank