629
FZMY50 PGUM 010459
CWFGUM

Coastal Waters Forecast for the Mariana Islands
National Weather Service Tiyan GU
259 PM ChST Thu Oct 1 2026

Marianas Waters out to 40 nautical miles

PMZ150-012115-
259 PM ChST Thu Oct 1 2026

.Synopsis for Marianas Waters...
Strong to Tropical Storm force westerlies will shift to southwest
Friday. Combined seas of 6 to 8 ft this evening will rapidly
increase to as high as 20 ft by Friday as Tropical Storm Choi-wan
(26W) approaches the northern CNMI and brings elevated southwest
monsoon swell to the Marianas. For Saipan and Tinian, a Tropical
Storm Warning remains in effect. For Guam and Rota, frequent gale
force gusts could lead to a Gale Warning. A Gale Watch has been
issued for Guam and Rota for the potential for frequent gale
gusts. Mariners should continue monitoring the forecast for
changes in the coming days.

$$

PMZ151-152-012115-
Guam Coastal Waters-Rota Coastal Waters-
259 PM ChST Thu Oct 1 2026

...SMALL CRAFT ADVISORY IN EFFECT FROM LATE THIS AFTERNOON
THROUGH EARLY FRIDAY MORNING...
...GALE WATCH IN EFFECT FROM LATE TONIGHT THROUGH SATURDAY
AFTERNOON...
...HAZARDOUS SEAS WATCH IN EFFECT FROM SATURDAY AFTERNOON THROUGH
SUNDAY AFTERNOON...

.TONIGHT...West wind 20 to 25 kt with occasional gusts to 35 kt.
Seas 6 to 8 ft, building to 9 to 11 ft. Wave Detail: West 8 ft at
8 seconds, southwest 6 ft at 8 seconds and north 4 ft at 11
seconds. Scattered showers with isolated thunderstorms.
.FRIDAY...Southwest wind 30 kt with frequent gusts to 40 kt
possible. Seas 12 to 14 ft. Scattered showers with isolated
thunderstorms.
.FRIDAY NIGHT THROUGH SATURDAY NIGHT...Southwest wind 30 kt with
frequent gusts to 40 kt possible. Seas 13 to 17 ft. Scattered
showers with isolated thunderstorms.
.SUNDAY...Southwest wind 20 to 25 kt with occasional gusts to 35
kt. Seas 12 to 15 ft. A chance of showers with a slight chance of
thunderstorms.
.MONDAY...Southwest wind 20 to 25 kt with occasional gusts to 35
kt. Seas 10 to 13 ft. Wave Detail: West 10 ft at 9 seconds,
southwest 8 ft at 9 seconds and northwest 3 ft at 13 seconds. A
chance of showers with a slight chance of thunderstorms.
.TUESDAY...Southwest wind 15 to 25 kt. Seas 8 to 10 ft. Wave Detail:
West 8 ft at 9 seconds, southwest 5 ft at 7 seconds and northwest
3 ft at 13 seconds. A chance of showers with a slight chance of
thunderstorms.

$$

PMZ153-154-012115-
Tinian Coastal Waters-Saipan Coastal Waters-
259 PM ChST Thu Oct 1 2026

...TROPICAL STORM WARNING IN EFFECT...

.TONIGHT...West tropical storm force wind to 35 kt with gusts to
50 kt. Seas 7 to 9 ft, building to 11 to 13 ft. Widespread locally
heavy showers and isolated thunderstorms.
.FRIDAY...Southwest tropical storm force wind to 35 kt with gusts
to 55 kt. Seas 14 to 16 ft. Widespread locally heavy showers with
isolated thunderstorms.
.FRIDAY NIGHT...Southwest tropical storm force wind to 35 kt with
gusts to 50 kt. Seas 15 to 18 ft. Widespread locally heavy
showers with isolated thunderstorms.
.SATURDAY...Southwest tropical storm force wind to 35 kt with
gusts to 45 kt. Seas 16 to 19 ft. Scattered showers with isolated
thunderstorms.
.SATURDAY NIGHT...Southwest wind 25 to 30 kt with gusts to 40 kt.
Seas 16 to 19 ft. Scattered showers with isolated thunderstorms.
.SUNDAY...Southwest wind 20 to 25 kt with gusts to 35 kt. Seas 14
to 17 ft. Scattered showers with a slight chance of
thunderstorms.
.MONDAY...Southwest wind 20 to 25 kt with gusts to 35 kt. Seas 12
to 15 ft. A slight chance of showers and thunderstorms.
.TUESDAY...Southwest wind 15 to 25 kt. Seas 8 to 10 ft. Wave
Detail: West 9 ft at 9 seconds, southwest 5 ft at 7 seconds and
northwest 3 ft at 13 seconds. A chance of showers with a slight
chance of thunderstorms.

$$