- For the contiguous United States, the average temperature for
September was 67.5°F (19.7°C), which was 2.1°F
(1.2°C) above the 20th century mean and the eighth warmest
September on record, based on preliminary data.
- Unlike August, no states set
record average temperatures during September. Most of the Lower 48
states had monthly averaged temperatures above normal, and no
states were below the normal average temperature for the
- Louisville, KY set a record high average temperature of
76.3°F (24.6°C) during September and both Key West, FL
and Washington, D.C. had the third warmest average temperature for
the month on record. Raleigh-Durham International Airport (NC)
reported a high of 101°F (38°C) on September 10, the
latest date in a calendar year with the maximum greater than 100
degrees since records began in 1944.
- At least 60 new high temperature records were set in the
Northeast region in September, the most notable in Caribou, ME on
September 25th. The new record of 83°F (28°C) was
10°F (5.6°C) warmer than the previous record set in
- Record high maximum and minimum temperature records were set in
Missouri, Illinois, Indiana, Wisconsin, Michigan and Kentucky
during the first five days of September. Brookville, Indiana
reached an unseasonably-warm 98°F (37°C) on September 5.
In contrast, record lows were set in the East North Central and
northern Central regions on September 15 after the passage of a
strong cold front.
- Nome, AK was completely frost free for the months of June,
July, August and September. On October 1st, the temperature dipped
to 32°F (0°C), ending the 2nd longest frost-free season
in Nome's 100+ years of climate record keeping. The longest
frost-free season occurred back in 1989.
- Although no new low precipitation records were set, this was
the 22nd driest September in the 1895—2007 record. An average
of 2.1 inches (53 mm) fell across the contiguous U.S. this month,
which is 0.4 inches (10 mm) below average.
- The widespread warmth and below-average rainfall in September
led to an expansion of drought in the Southeast and parts of the
mid-Atlantic and Ohio Valley. At the end of September, drought
affected approximately 62% of the Southeast and 43% of the
contiguous U.S., according to the federal U.S. Drought Monitor. In
addition, 28% of the contiguous U.S. was in moderate to extreme
drought. For more information on drought during September, please
visit the U.S. Drought Watch
- Drought and mild temperatures have pushed Lake Superior's water
level to its lowest point on record for this time of year,
continuing a downward trend across the Great Lakes. Preliminary
data show Superior's average water level dipped 1.6 inches (41 mm)
beneath the previous low for the month reached in 1926, according
to NOAA's Great Lakes Environmental Research Laboratory.
- All the Great Lakes, which together make up about 20% of the
world's fresh surface water, have been in decline since the late
1990s. Lakes Huron and Michigan were about 2 feet (610 mm) below
their long-term average levels, while Lake Superior was about 20
inches (510 mm) off, Lake Ontario 7 inches (180 mm) below, and Lake
Erie a few inches (tens of mm) below normal in September.
- September brought large amounts of precipitation to Minnesota,
Missouri and the Upper Peninsula of Michigan, which received an
estimated 10 inches (254 mm) of rainfall. These heavy rains have
alleviated much of the Extreme Drought conditions in the Upper
Midwest, although states in the Southern Midwest have seen little
relief. Approximately 88% of the state of Kentucky was under
Extreme Drought conditions by the end of the month.
- Precipitation totals in the Northeast averaged 61% of normal,
with all states reporting below-average rainfall. About half of the
counties in Maryland and Pennsylvania are under a drought watch,
many areas in New York reported record low reservoir levels, dried
up wells and farm ponds, and water restrictions are in place in
communities throughout the Northeast.
- As of September 25, Pasadena, CA experienced its driest year
since records began in 1878, and the mayor has asked Pasadena
residents to voluntarily conserve water. In early September, Long
Beach, CA imposed the most severe water restrictions seen in the
region in years, including forcing residents to cut back on
watering their lawns.
Other Items of Note
- September 2007 was the 12th wettest on record in Anchorage, AK
with 4.30 inches (109.2 mm) of precipitation, which is 1.43 inches
(36.3 mm) above normal.
- September began with numerous large fires burning across the
Northern Rockies, but fire activity dissipated by the end of the
month as rain and high elevation snow dampened the region. As of
early October, more than 8 million acres (32,000 km²) had
burned across the nation, most of it in the West.
- Dry conditions in northern Alaska during September contributed
to a very large, late-season wildfire. The Anaktuvuk River
wildfire, caused by lightning, burned over 250,000 acres (1000
km²), setting a record for the largest fire on the North
- Tornadoes occurred in conjunction with each of the three
tropical systems that affected the southeastern U.S. (Gabrielle,
Humberto, and Tropical Depression 10). Between September 10 and 22,
each of the states in the Southeast region reported tornadic
- La Niña conditions were present in the tropical Pacific
Ocean by the end of September. Sea-surface temperature (SST)
anomalies have become increasingly negative in the central and
eastern equatorial Pacific and remain positive in the western
Pacific. Nearly all of the dynamical and statistical models are
forecasting weak-to-moderate La Niña conditions strengthening
and persisting during the next several months. A developing La
Niña may result in wetter than normal conditions in the
Pacific Northwest and drier than normal conditions in the
southwestern U.S. in the fall. To be considered a full-fledged La
Niña episode, a negative Oceanic Niño Index (ONI) less
than or equal to -0.5°C must be exceeded for a period of at
least five consecutive months. The most recent ONI value
(June—August 2007) is -0.2°C. For additional information
on ENSO conditions, please visit the NCDC ENSO Monitoring page and the
NOAA ENSO Advisory.
For additional details about recent temperatures and
precipitation across the U.S., see the Monthly and
Seasonal Highlights section below and visit the September Climate Summary page. For
information on local temperature and precipitation records during
the month of September, please visit NCDC's Extremes page. For details and graphics on
weather events across the U.S. and the globe please visit
NCDC's Global Hazards page.