236
FXPQ50 PGUM 180919
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
719 PM ChST Tue Aug 18 2026

.Marianas Synopsis...
Visible satellite imagery shows mid- to upper-level cloud debris,
low-end scattered showers, and isolated pockets of convection,
especially in the CNMI coastal waters. Altimetry indicates combined
seas of 4 to 6 ft.

&&

.Discussion...
The Marianas are located within a surface trough extending from
Invest 92W which is currently located east of Chuuk. The
northeasterlies are shifting to northwesterlies, leaving the Marianas
within directional convergence. Therefore, scattered showers and
isolated thunderstorms are forecasted tonight through the next
several days. Winds will pick up from light and variable to north
around 10 mph after midnight, and will slightly increase to gentle to
moderate. Depending on the intensity and track of Invest 92W, an
asymmetric wind field may bring light wind conditions to the Marianas
briefly at the end of the work week before increasing through the
first half of next week. Current model guidance indicates a passage
through the far northern Marianas, placing Guam and the CNMI within
its monsoonal tail. Thus, elevated winds, increasing showers, and
thunderstorms are a possibility from the weekend through midweek.
Residents of the Marianas should continue to monitor the forecast.

&&

.Marine...
Combined seas of 4 to 6 ft will continue for the next several days
comprised of a primary west and a secondary northeast swell. The
westerly swell will slightly decrease by a foot on Wednesday before
picking back up the following day. There is a moderate risk of rip
currents along north- and west-facing reefs and a moderate risk of
lightning through the week. Towards the end of the work week,
depending on Invest 92W, a long-period, easterly to northeasterly
swell may envelop the region. Rip currents may become dangerous along
east- and north-facing reefs next week, and a surge in winds may
warrant hazardous conditions to small craft. Since there is high
uncertainty regarding these impacts as they relate to Invest 92W,
marine interests should continue to monitor the forecast in the
coming days.

&&

.Tropical Systems...
A tropical disturbance, known as JTWC`s Invest 92W, is centered near
8N155E halfway between Chuuk and Pohnpei. 92W is now a subject of a
Tropical Cyclone Formation Alert by JTWC, which means that tropical
cyclone development is expected within the next 24 hours. 92W
continues to exhibit a sustained westerly push along the southern
peripheries, with 15 to 25 kt winds embedded within this inflow zone
as indicated by most recent ASCAT passes. This will help 92W to
continue consolidating over the next day or so, moving northward as
the monsoon surge continues to drive moisture into the system. Once
92W crosses 10N, it will shift moreso to the northwest as the
northern flanks build as well, with the environment north of 10N
being much more conducive for cyclogenesis than its current location.
The most recent storm trek consensus is a passage across the
northernmost islands of the Marianas by late this week, but this
remains highly uncertain at this time due to 92W`s state and volatile
environmental conditions around the Marianas. For more information
regarding impacts to Pohnpei and Chuuk, refer to the Special Weather
Statement SPSPQ1 for Pohnpei, and Special Weather Statement SPSPQ2
for Chuuk, respectively. For more information on Invest 92W, see
bulletins issued by JTWC under WMO headers WTPN21 PGTW for the
Tropical Cyclone Formation Alert, and ABPW10 PGTW for the prognostic
reasoning.

&&

.Eastern Micronesia...
Invest 92W continues to slowly organize northwest of Pohnpei/east-
northeast of Chuuk. Satellite imagery shows the system continues to
be asymmetric, with convection tied to the west-southwest semicircle
of the system. However, JTWC (the Joint Typhoon Warning Center) has
recently upgraded 92W to a TCFA (Tropical Cyclone Formation Alert -
meaning the development of a tropical cyclone is likely within the
next 24 hours). The scatterometer data showed that 20 to 25 knot wind
bards are present near Pohnpei roughly 1 degree or 60 miles away. We
had some in-house discussion as to when 92W`s wind field will
strengthen and burgeon enough to enter the western coastal waters of
Pohnpei. Given the latest-available scatterometer data from 2238Z
(10:38 AM ChST) showed only a small area of 20 to 25 knot winds,
which was co-located with heavier convection. Thus, conceptionally
the larger wind field is closer to 15 knots, which is what the
midnight scatterometer pass showed as well. As such, the coastal
forecast has 15 to 20 knot winds, increasing into the 20 to 25 knot
range by sunrise Wednesday morning. This is to account for any
potential burgeoning of the wind field as 92W slowly strengthens, as
it continues to move slowly west. There`s some potential for locally
heavy rainfall, which could allow for an isolated gust or two up to
30 knots remaining possible through then. With this in mind, a Small
Craft Advisory was issued for Pohnpei, with it not going into effect
until 3 AM local time.

The next forecast dilemma was with the Special Weather Statement.
This had mentioned that locally heavy rainfall, locally heavy
rainfall and wind gusts to 35 knots through Wednesday. Thus far, no
reported gusts near or over 25 knots have been observed, but this
can`t completely be ruled out, if robust convection with -80 deg. C
cloud top temperatures develop (as the cloud tops would be ~55,000
feet tall, allowing for enhanced downdraft potential), or if 92W
strengthens and consolidates faster than expected. This is expected
to occur, with a gradual northwest change of direction and increased
forward speed anticipated to begin in the next 24 to 48 hours. Until
then, there remains some question as to when 22 knot winds will
overspread Poihnpei`s coastal waters, or if it`ll continue to shift
north and west, away from Pohnpei. Thus, the Small Craft Advisory
was issued with some forecast concerns regarding these temporal
questions.

Regarding heavy rainfall at Pohnpei, the last 18 hours of satellite
observations show cloud top temperatures have struggled to surpass -50
deg. C, indicating only light to moderate showers have developed near
Pohnpei and Kosrae. This leaves some concerns about weather to extend
the previously issued Special Weather Statement for both locations.
will defer to the evening shift to address this as Kosrae is looking
less likely of a concern, while Pohnpei will heavily depend on 92W`s
behavior the next 24 hours. At Majuro, the monsoon trough is nearby
just to your south, but close enough to retain scattered shower
coverage for much of the period.

As for marine conditions, strong to fresh winds may develop at Pohnpei,
with seas of 6 to 9 feet possible, mainly across the western waters.
These seas will gradually decrease in height as we head through the
week. At Kosrae and Majuro, light to gentle winds and seas of 5 to 7
feet will continue through much of the week.

&&

.Western Micronesia...
Satellite observations show partly cloudy skies across Palau and
Yap, and mostly cloudy skies across Chuuk. Altimetry shows combined
seas between 4 and 6 feet across Palau and Yap, and 6 to 8 feet
across Chuuk.

Quiet conditions will continue tonight for Palau and Yap and then
unsettled weather will move into Yap tomorrow. Some of these showers
and thunderstorms are already impacting eastern portions of Yap
State this evening. Shower coverage will expand into Palau Wednesday
night and especially Thursday. A monsoonal tail will build across the
region by Thursday, bringing locally heavy showers that could lead
to flooding. At this time mudslides appear unlikely on the onset, but
if heavy rainfall continues into the weekend, conditions could
become favorable to mudslides. Shower and thunderstorm coverage
should begin to trend downward early next week.

Invest 92W has steadily organized today and is now subject to the
Joint Typhoon Warning Center`s Tropical Cyclone Formation Alert.
Numerous to widespread showers and isolated to scattered
thunderstorms are seen along the southern semicircle of 92W.
Additional rainfall amounts of 4 to 6 inches are possible through the
week. These rainfall amounts could result in flash flooding and
potential mudslides. Towards the latter half of the week, a monsoon
surge will develop and continue to impact Chuuk with gusty winds and
seas hazardous to small craft. Residents across Chuuk State should
monitor local forecasts and heed advice of emergency managers when
heavy rainfall occurs. Cross equatorial flow will move into the
region this weekend, which will keep showers chances scattered
(30-50%), but will generally bring drier weather across the region.

Combined seas are currently between 6 and 8 feet across Chuuk and 4
to 6 feet across Palau and Yap. Combined seas look to remain benign
across Palau and Yap through Thursday and then look to become choppy
on Friday and going into the weekend. Surf could become hazardous
along west facing reefs of Yap this weekend. A Small Craft Advisory
is in effect for Chuuk tonight for frequent gusts of 30 knots through
Wednesday and then for winds up to 25 kt, occasional gusts to 35
knots, and seas of 7 to 10 feet Wednesday night through Friday
afternoon. Marine conditions look to taper down this weekend, but
seas could be hazardous to small craft for an extended period of time
depending on the track of Invest 92W.

&&

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

$$

Marianas: Mesa
Tropical: Montvila
East Micronesia: Doll
West Micronesia: Williams