169
AXPQ20 PGUM 120123
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1123 AM ChST Wed Mar 12 2025

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...

NEAR EQUATORIAL TROUGH...
A near-equatorial trough enters the region near 3N130E and then runs
along or just north of the equator, passing well south of Palau, and
to a weak circulation on the equator near 142E. Moderate to heavy
showers and a few thunderstorms are found along the trough between
the equator and 4N, with most of the showers and thunderstorms ending
west of the circulation. Both the near-equatorial trough and
circulation will stay along the equator through the week with showers
and thunderstorms persisting. The circulation is expected to
eventually weaken within the trough.

TRADE-WIND TROUGHS...
A broad trade-wind trough extends from the equator near 150E and
curves north-northeast into Chuuk State and ending just east-southeast
of Chuuk Lagoon near 7N154E. Numerous to widespread showers and
isolated thunderstorms are found along the trough, with some showers
expected to move into Weno this afternoon as the trough moves west,
continuing through Chuuk State and later into the outer islands of
Yap State. Ahead of the trough between 7N and 10N from 151E to 137E,
satellite imagery shows a weak band of convergence generating
scattered showers and isolated thunderstorms just north of most of
the outer islands of Yap and Chuuk State and ending southeast of Yap
Proper. This area of convergence is expected to be absorbed by the
trade-wind trough as the trough moves westward.

TUTT...
The tropical upper-tropospheric trough (TUTT) still sits over Kosrae
and the Marshall Islands, but appears to have paused in its eastward
motion that was seen 24 hours ago. A TUTT cell, or upper-level low,
has started to cut off from the TUTT with satellite water vapor
showing a cell just south of Kosrae. This TUTT cell is expected to
linger near Kosrae and Pohnpei States tonight before eventually being
absorbed by westerly flow to the north. Divergence south of the TUTT
axis is likely enhancing convection along the ITCZ that extends over
the southern and central Marshalls, including near Majuro and just
south of Kwajalein, and extending across Kosrae and Pohnpei States
helping to produce thunderstorms and gusts to around 30 mph. While
the influence of the TUTT will wane over the next couple of days,
convection is anticipated to remain across the area with the
activity of the ITCZ, see below.

OTHER SYSTEMS...

COLD FRONT, SHEAR LINE...
A cold front curves southwest through 25N172E to near 16N150E, then
continues as a shear line across the Marianas between Anatahan and
Saipan, to near 13N132E. Patchy clouds and showers are found along
and up to 200 miles northwest of these features. Midday scatterometry
shows winds of 15-20 mph south of the boundaries with a band of
20-30 mph winds to the north of the shear line and cold front. The
shear line looks to be stalling just north of Saipan. The presence of
the shear line will be noted with increased cloudiness, showers,
stronger gusts, and increasing northeast swell.

The low pressure system that the cold front attaches to, well
north-northeast of the region, has generated a pulse of long-period
northerly swell that will be moving through the region, with the
larger swell expected across the Marianas, Chuuk, Pohnpei, and
Kosrae State, and the Marshall Islands. Swell heights are expected to
be lower for Yap and Palau and more northeast in direction.
Satellite altimetry shows sea heights around 10 to 13 feet between
20N and 25N, from 150E to 175E, likely marking the leading edge of
the higher swell. As this swell moves through, surf will build and
potentially become hazardous with surf of 9 feet or higher. This
swell is also moving through the region around the same time of the
full moon, so high tides will be elevated, increasing the risk for
minor coastal inundation, especially the low lying islands/atolls of
the northern Marshall Islands.

...ITCZ...
Showers and thunderstorms are developing from Majuro and across
Kosrae and Pohnpei States, between 4N and 8N from 175E to 154E, where
it then merges with the trough in Chuuk State. Scatterometry shows a
wind of 20-25 mph along the line of convection within the ITCZ with
gusts likely approaching around 30 mph. Latest model guidance
suggests this solidified band of showers and thunderstorms is
expected to span the region from Chuuk State to the Marshall Islands,
mainly between 4N and 8N, slowly shifting westward as it follows the
trade-wind trough in Chuuk State, leading to an increase in showers
and thunderstorms in Yap State the next couple of days and
potentially Palau by the weekend.

$$

Schank