757
FXPQ50 PGUM 260806
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
606 PM ChST Thu Sep 26 2024

.Marianas Synopsis...
Satellite imagery shows partly cloudy to mostly cloudy skies, with
radar showing spotty showers near the islands and coastal waters,
and becoming more scattered to numerous to the east, around 95W,
northeast of Saipan. Gentle to moderate west to southwest winds
extend from Saipan to Guam, while winds for the far northern Islands
are more northerly, becoming easterly further north up the chain.

&&

.Discussion...
Invest 95W is the primary feature and it is currently centered
northeast of Saipan near 16N147E, outside of the coastal waters.
Most of the showers and thunderstorm activity is around 95W, leaving
showers spotty across the islands this evening. The strongest winds
are also still on the northern and eastern edge of 95W so winds
across the Marianas have been fairly gentle to moderate. Still
expecting 95W to trek northwestward over then next few days, passing
north of Saipan and through the far northern Mariana Islands. The
exact path it will take is still uncertain as showers and
thunderstorms are still displaced southeast of the low-level
circulation visible on satellite, making it difficult to predict the
overall motion. A more northward path will decrease the potential for
showers and thunderstorms on Friday for Saipan and Tinian, and
especially for Guam and Rota along with decreased cloud cover. A
slight southern path will increase the potential for numerous locally
heavy showers and gusty winds on Friday for Saipan and Tinian, while
increasing confidence for at least scattered showers and isolated
thunderstorms for Guam and Rota. The latest model runs of the GFS and
ECMWF have favored a slightly more northern path, but this could be
an outlier, so current forecast blends the most recent runs with our
previous forecast.

We currently expect isolated showers to become scattered overnight
along with an increasing chance for thunderstorms. As 95W pass north
of Saipan, showers will become numerous showers with occasional
gusty winds around Saipan and Tinian, with showers becoming much more
scattered southward towards Rota and Guam; though thunderstorms and
occasional gusts will still be possible near heavier showers. As 95W
passes west of the Marianas and into the Philippine sea, showers
will decrease across all of the Marianas Saturday and into Sunday,
along with west to southwest winds turning towards the south and then
becoming southeast to east. For next week, expect a fairly quiet
trade-wind pattern, with periods of scattered showers possible as
weak trade-wind troughs move through the Marianas.

&&

.Marine...
The circulation known as Invest 95W will gradually move to the north
of Saipan and through the far northern Mariana Islands over the next
couple of days. This will bring southwest to west winds through
Friday, which will veer southerly this weekend and return to
easterly trades by early next week. Winds are expected to be light
to moderate for Guam and Rota and gentle to fresh for Tinian and
Saipan. Heavier showers may bring occasional fresh to strong gusts,
possibly near gale for Tinian and Saipan Friday and Friday night.
Seas 3 and 5 feet may occasionally reach 6 or 7 feet Friday through
Saturday, based on an increase in wind waves and choppy seas induced
by 95W.

&&

.Tropical systems...
JTWC Invest 95W is located northeast of Saipan near 16N147E, and is
still subject of a Tropical Formation Alert, meaning is likely to
develop into a tropical cyclone (tropical depression) within 24
hours. Scatterometer shows the strongest winds (15-25 kt) are still
on the eastern edge of the circulation, while for most of the day,
satellite imagery showed an exposed low-level circulation northeast
of Saipan and east of Anatahan, while most of the convection was
displaced to the southeast, where the mid-level vorticity was the
strongest, according to the latest CIMSS satellite analysis. The most
recent satellite imagery is starting to show convection developing
over the low-level circulation which could be a sign that 95W is
shifting northward over that circulation, favoring a slightly
northern trek that the GFS and ECMWF started to show in the latest
runs. Please see WTPN21 PGTW JTWC bulletin for further information.

The disturbance that has been north of Yap over the past few days, is
now referred to as Invest 98W. Scatterometer data indicated an ill-
defined circulation near 14N137E with 15 to 25 kt winds, mainly south
of the center. Overall convection is disorganized and little to no
development is expected as it slowly drifts north, possible becoming
absorbed into 95W.

&&

.Eastern Micronesia...
Little has change from the previous forecast. A light wind pattern
extends across the region with showers developing along weak troughs
moving through the flow. Pohnpei is seeing some of these showers
while showers are very spotty around Kosrae and Majuro. Over by
Majuro there is a very broad and weak circulation to east of the
Marshall Island, but it is expected to open back into a trough as it
moves through Majuro, increasing showers around Majuro Friday
afternoon. Weak winds will be supportive of island effect showers
during the afternoon hours, especially at the larger islands such as
Pohnpei. Through the weekend, winds are expected to remain fairly
light, with periods of scattered showers, associated with troughs
that pass near the islands. Late this weekend and early next week,
models still support weak trade-wind convergence developing near the
Marshall Islands and Majuro and then pushing westward to Pohnpei by
the middle of next week. This should increase the potential for
showers across the region while also slightly boosting the easterly
winds.

Little has changed regarding marine conditions as seas are still
expected to hover between 3 and 4 feet, a mix of east and southeast
swell and a small northerly swell. The southeasterly swell is
expected increase a foot or two over the weekend or early next week
as it moves in from southern hemisphere, but it is not expecting to
cause any impacts.

&&

.Western Micronesia...
A monsoon-like trough extends north of Palau, through a circulation
northwest of Yap near 14N137E, now referred to as 98W, and ending at
Invest 95W near the Marianas. Convergent west-southwesterlies south
of these features continue to bring scattered showers across Palau
and Yap. Farther east, satellite shows scattered showers alongside
convergent northeast trades ahead of a broad trough moving across
Chuuk this afternoon. As these features continue moving west-
northwest, Invest 98W is expected to slowly drift northward away from
the region with little to no development expected, off-and-on trade
showers continue for Chuuk and the ridge in between these two regimes
will aim to suppress showers for Yap and Palau this weekend.
However, it will be possible that the light and variable winds may
give a chance for afternoon island-effect showers. By next week,
Palau and Yap is expected to transition to a trade- wind pattern,
keeping scattered showers in the forecast through midweek.

Benign marine conditions continue. Light to gentle winds and pulses
of minor north to northeast swell over the next several days will
slightly increase surf along north facing reefs. Combined seas of 1
to 3 feet increase to 2 to 4 feet by the weekend.

&&

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

$$

Marianas: Williams/Schank/Cruz
Tropical: Schank
Eastern Micronesia: Schank
Western Micronesia: Cruz