364
FZMY50 PGUM 201748
CWFGUM

Coastal Waters Forecast for the Mariana Islands
National Weather Service Tiyan GU
348 AM ChST Fri Aug 21 2026

Marianas Waters out to 40 nautical miles

PMZ150-210900-
348 AM ChST Fri Aug 21 2026

.Synopsis for Marianas Waters...
A Tropical Storm Watch remains in effect for Tinian and Saipan.
Light to gentle northeast winds and combined seas of 4 to 6 feet
will continue to increase today ahead of Tropical Storm Saudel,
particularly for Tinian and Saipan. Conditions will quickly
deteriorate late tonight with southwest winds increasing tonight
and tropical storm force winds possible after midnight for Tinian
and Saipan through Saturday night or Sunday. Locally higher wind
waves and increasing east to northeast swell will build seas that
can exceed hazardous levels of 10 feet for the coastal waters of
Tinian and Saipan late tonight and over the weekend. For Guam and
Rota, expect elevated seas of 7 to 9 feet over the weekend.

$$

PMZ151-152-210900-
Guam Coastal Waters-Rota Coastal Waters-
348 AM ChST Fri Aug 21 2026

.TODAY...Variable wind 5 kt, becoming west 5 to 10 kt in the
afternoon. Seas 4 to 6 ft. Wave Detail: East 4 ft at 10 seconds,
west 3 ft at 8 seconds and west 2 ft at 4 seconds.
.TONIGHT...Southwest wind 5 to 15 kt. Seas 5 to 7 ft. Wave
Detail: East 5 ft at 9 seconds, west 3 ft at 8 seconds, southwest
3 ft at 4 seconds and south 2 ft at 8 seconds. Isolated
thunderstorms.
.SATURDAY...Southwest wind 10 to 20 kt. Seas 6 to 8 ft. Wave
Detail: Northeast 5 ft at 9 seconds, southwest 4 ft at 5 seconds,
southwest 4 ft at 8 seconds, and south 3 ft at 8 seconds.
Scattered showers with isolated thunderstorms.
.SATURDAY NIGHT...Southwest wind 15 to 25 kt. Seas 7 to 9 ft.
Wave Detail: North 5 ft at 9 seconds, southwest 6 ft at 6
seconds, southwest 4 ft at 8 seconds, and south 3 ft at 8 seconds.
Scattered showers with isolated thunderstorms.
.SUNDAY...Southwest wind 15 to 25 kt. Seas 7 to 9 ft. Wave
Detail: North 5 ft at 9 seconds, southwest 5 ft at 6 seconds,
southwest 4 ft at 8 seconds and south 3 ft at 8 seconds. A chance
of showers with a slight chance of thunderstorms.
.MONDAY AND TUESDAY...Southwest wind 10 to 15 kt. Seas 6 to 8 ft.
Wave Detail: Southwest 4 ft at 8 seconds, northwest 4 ft at 9
seconds, southwest 3 ft at 4 seconds and south 3 ft at 8 seconds.
A chance of showers with a slight chance of thunderstorms.

$$

PMZ153-154-210900-
Tinian Coastal Waters-Saipan Coastal Waters-
348 AM ChST Fri Aug 21 2026

...TROPICAL STORM WATCH REMAINS IN EFFECT...

.TODAY...North to northeast wind 5 to 10 kt. Seas 4 to 6 ft,
increasing to 6 to 8 ft in the afternoon. Wave Detail: East 6 ft
at 10 seconds, west 3 ft at 8 seconds and north 2 ft at 4 seconds.
Scattered showers and isolated thunderstorms developing around
noon. Locally heavy showers possible.
.TONIGHT...Tropical storm conditions possible after midnight.
West wind 10 to 20 kt increasing to 25 to 35 kt with gusts to 50
kt. Seas 7 to 9 ft, increasing to 9 to 10 ft. Wave Detail: East 7
ft at 10 seconds, west 7 ft at 4 seconds, west 3 ft at 8 seconds
and south 2 ft at 8 seconds. Scattered showers, becoming numerous
and heavy after midnight. Isolated thunderstorms. Locally heavy
showers possible.
.SATURDAY AND SATURDAY NIGHT...Tropical storm conditions
possible. Southwest to west wind 30 to 40 kt with gusts to 50 kt.
Seas 8 to 12 ft. Wave Detail: Northeast 7 ft at 9 seconds, west 7
ft at 6 seconds, southwest 4 ft at 8 seconds and south 4 ft at 8
seconds. Periods of rain, widespread heavy showers and scattered
thunderstorms.
.SUNDAY...Tropical storm conditions possible. Southwest wind 30
to 40 kt with gusts to 50 kt. Seas 8 to 10 ft. Wave Detail: North
6 ft at 10 seconds, southwest 7 ft at 6 seconds, southwest 4 ft at
8 seconds and south 3 ft at 8 seconds. A chance of showers with a
slight chance of thunderstorms. Periods of rain, widespread heavy
showers and scattered thunderstorms.
.MONDAY AND TUESDAY...Southwest wind 5 to 15 kt. Seas 5 to 7 ft.
Wave Detail: Southwest 4 ft at 8 seconds, northwest 4 ft at 9
seconds, southwest 3 ft at 4 seconds and south 3 ft at 8 seconds.
A chance of showers with a slight chance of thunderstorms.

$$