U.S. WEATHER September hurricanes kept twisters coming

August was also a banner month for tornadoes.
SCRIPPS HOWARD
September's hurricanes helped spawn the most tornadoes reported for the month in the United States in at least 50 years, government experts report.
Preliminary reports indicate 247 twisters were reported during September, compared with 139 September storms in 1967, the next highest tally. The average number of tornadoes during September is 47.
The storm-tossed month followed a record-breaking 173 tornadoes reported in August, also largely due to tropical storms and hurricanes.
"The extremely active tropical storm season can be partially blamed for the high number of tornado reports," said Dan McCarthy, warning coordination meteorologist at the National Oceanic and Atmospheric Administration's Storm Prediction Center in Norman, Okla.
The final number of storms for each month may change as officials from the National Weather Service continue to complete damage assessments and other evidence of whether a tornado actually touched down.
The cause
Hurricanes Frances, Ivan and Jeanne affected the Southeast and Mid-Atlantic states during the month. Tornadoes frequently form in the northeast quadrant of advancing tropical systems or their remnants.
"This is the sector where wind shear has its greatest effect on storms in the rain bands around the systems," McCarthy said. And the track of the storms north along the spine of the Appalachians allowed them to continue drawing moisture and energy from the Atlantic.
With 117 reported twisters, Hurricane Frances produced the most tornadoes ever for a single storm, striking from Florida north into Maryland and West Virginia.