Name: Tropical Storm in Guam, September 21, 2010
Start: 2010-09-21T04:00
End: 2010-09-21T18:00
Location: Guam

The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 1

Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.

What happened

The episode as NWS GUM wrote it up.

At about 0400 GST on the 21st of September, Tropical Depression 13W intensified into Tropical Storm Malakas sbout 60 miles northwest of Agrihan and 90 miles northwest of Pagan Island in the Commonwealth of the Northern Mariana Islands. Tropical Storm Malakas moved erratically during the day about 50-70 miles northwest and west of the two islands...then moved off to the west-northwest that evening and overnight. No wind measurements are available from either island, but satellite data and data from Air Force reconnaissance aircraft indicate that winds up to 40 mph likely affected both Agrihan and Pagan during the day on the 21st. No damage or injuries were reported.

What forecasters said that day

The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Guam wrote its last area forecast discussion before the first event at Sep 20, 7:45 AM UTC, 10 hours 15 minutes earlier.

Area forecast discussion, Sep 20, 7:45 AM UTC, 10 hours 15 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TIYAN GU
545 PM CHST MON SEP 20 2010

.SYNOPSIS...
PGUA WSR-88D SHOWS SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS
SOUTH OF A TROPICAL DISTURBANCE MOVING THROUGH THE MARIANAS
WATERS. THE TROPICAL DISTURBANCE IS CENTERED NEAR 19N AND
146E...AND REMAINS THE SUBJECT OF A TROPICAL CYCLONE FORMATION
ALERT RECENTLY RENEWED BY THE JOINT TYPHOON WARNING CENTER.
ELSEWHERE...TRADE-WIND CONVERGENCE IS COMBINING WITH UPPER-LEVEL
DIVERGENCE SOUTH OF THE TROPICAL UPPER TROPOSPHERIC TROUGH /TUTT/
TO CREATE SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS NEAR YAP
AND PALAU BETWEEN 3N AND 17N FROM 130E TO 143E AND NEAR KOSRAE
AND THE MARSHALL ISLANDS BETWEEN 5N AND 11N FROM 159E TO 171E.

&&

.DISCUSSION...
INVEST AREA 90W HAD ITS TROPICAL CYCLONE FORMATION ALERT RENEWED.
IF IT MAINTAINS THE DEEP CONVECTION IT HAS HELD ON TO FOR A GOOD
12 HOURS NOW IT WILL COOK OFF AND BECOME A TROPICAL CYCLONE. BY
THE TIME IT ACHIEVED GALE FORCE WINDS IT SHOULD BE WEST OF THE
MARIANAS THOUGH...SO STILL NO WATCHES OR WARNINGS ARE EXPECTED.
GFS40 MODEL SHOWS THAT 90W WAS UNDER 15 TO 20 KNOTS OF VERTICAL
SHEAR THIS MORNING. THAT SHEAR HAS SINCE RELAXED A BIT WHICH HAS
ALLOWED THE CONVECTION TO REMAIN MORE STABLE AND NEARER TO THE
CIRCULATION CENTER. THE SHEAR IS EXPECTED TO RELAX EVEN FURTHER
THIS EVENING SO WOULD NOT BE SURPRISED TO SEE IT WARNED ON WITHIN
THE NEXT 18 TO 21 HOURS. THE HEAVY RAIN IS NOW POISED TO PASS
NORTH OF SAIPAN INTO THE FAR NORTHERN MARIANAS. WENT AHEAD AND
REFRESHED THE SPECIAL WEATHER STATEMENT TO EMPHASIZE THIS. NOW
THAT THE SYSTEM IS MOVING AND THE WORST SHOWERS WILL MISS THE
PUBLIC AND COASTAL FORECAST ZONES SHORTENED THE SCATTERED SHOWERS
TO NOON TUESDAY INSTEAD OF TUESDAY EVENING. AFTER THE SYSTEM
PASSES BY SOME CLOUDS WILL REMAIN FOR A DAY OR TWO...THEN A
RETURN TO THE RATHER LACKLUSTER WET SEASON WE HAVE ALREADY BEEN
EXPERIENCING. NO OTHER CHANGES WERE NECESSARY AS THE PREVIOUS
GRID PACKAGE HAD A SIMILAR PHILOSOPHY.

&&

.EASTERN MICRONESIA...
EXTENSIVE CLOUDINESS AND SOME SHOWERS BETWEEN KWAJALEIN AND
POHNPEI IS ALL THAT REMAINS FROM THE BELT OF CONVECTION EARLIER
TODAY. SCATTERED SHOWERS ACROSS KOSRAE AND POHNPEI HAVE ENDED
WITH DRIER CONDITIONS EXPECTED THROUGH THE WEEKEND. GFS BUILDS
SOUTHEASTERLY FLOW ACROSS THE REGION WITH THE BULK OF CONVECTION
NORTH OF ALL LOCATIONS THROUGH SATURDAY.

&&

.WESTERN MICRONESIA...
SCATTERED SHOWERS FOR CHUUK WERE REDUCED TO ISOLATED TONIGHT AS
DEEP CONVECTION DISSOLVES ACROSS THE AREA TOWARDS POHNPEI.
SCATTERED SHOWERS COULD RETURN TOMORROW AS EASTERLY FLOW BUILDS
AND CONVERGES WITH THE SOUTHEAST FLOW NORTH AND WEST OF CHUUK.
SCATTERED SHOWERS AND THUNDERSTORMS EXIST WEST OF CHUUK IN
RELATION TO JTWC INVEST AREA 90W...WITH ITS CENTER NEAR PAGAN.
SHOWERS AND STORMS WEST OF CHUUK WILL MOVE OUT AS THE SYSTEM
MOVES NORTHWEST. A NORTH-SOUTH ORIENTED TROUGH BETWEEN YAP AND
PALAU HAS KEPT SHOWERS AND THUNDERSTORMS IN PLACE ACROSS THE
REGION TODAY. SOUTHERLY FLOW AND SHOWERS WILL GRADUALLY GIVE WAY
TO EASTERLY FLOW AND DRIER CONDITIONS BY TUESDAY NIGHT.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...NONE.
MARIANAS WATERS...NONE.
&&

STANKO/M. AYDLETT

Event by event

1 tropical storm. Local standard time, as filed.

Tropical Storm, Northern Marianas

When: September 21, 4:00 AM GST to 6:00 PM GST
Where: Northern Marianas forecast zone
Reported by: Emergency Manager

What these are

Tropical Storm: A tropical cyclone with sustained winds of 34 to 63 knots (39 to 73 mph).

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

More

Every storm in Guam in 2010 Every state in 2010 This day in weather history Warnings in Guam, September 2010 The 2010 hurricane season

Sources

NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 260065.