Hurricane Isaac's tornado production from late August through early September 2012

radar_tornado_couplet — A tornadic signature is seen in Jackson County, Mississippi as an eastern rainband from Hurricane Isaac slowly moves through the area late on August 29, 2012. This was the 7th tornado warning for the county of the day, with over 2 dozen such warnings in Ms. through that point in the mid-evening.

After hurricane Isaac made landfall across southern Louisiana late Tuesday August 28 and into early Wednesday, August 29, tornado warnings were seemingly up throughout most of the day that followed. Not a surprise, as tropical systems usually produce tornadoes, particularly those that make landfall across the northern Gulf of Mexico. That was just the beginning.

We’ve been keeping some running tallies going on Twitter, but as tornado verifications roll in, we’ll go ahead and keep track of them here as well. Additionally, I’ve assembled a look at each day of warnings, and some combined stats through the most recent full day of Isaac’s tornado producing life (September 3). As of publish, the system is nearly washed out, though it’s possible additional warnings and/or tornadoes may still come. If that’s the case, those stats will be updated as needed.

Past storms – Warnings/confirmed
Ivan (2004): 213 warnings / 118 tornadoes
Katrina (2005): 167 warnings / 59 tornadoes
Debby (2012): 62 warnings / ~20 tornadoes

There have been 19 tornado watches issued for Isaac: 2 in south Florida on the 26th into 27th, nine along the northern Gulf Coast states from August 28 through August 30, two in the Midwest on August 31, three in the Midwest and South on September 1, two from Kentucky to Mississippi on September 2, and one across parts of Alabama and Mississippi on September 3. Parts of southern Mississippi were under a tornado watch from 9: 45 a.m. Aug 28 through 10 p.m. August 30.

Over the entire period, Hurricane Isaac and its remnants caused 171 tornado warnings. The following National Weather Service offices, by order of the most products, issued warnings: New Orleans, La.; Mobile, Al.; Jackson, Ms.; Paducah, Ky.; Memphis, Tn.; Tallahassee, Fl.; Huntsville, Al.; Central Illinois, Il.; Melbourne, Fl.; St. Louis, Mo.; Louisville, Ky.; Tampa Bay, Fl.; Birmingham, Al.; Little Rock, Ar.; Miami, Fl.; Morristown, Tn.; Nashville, Tn.; Raleigh, NC; and Mount Holly, NJ.

Mississippi comes in with the most tornado warnings at 77. Alabama, Florida and Missouri all witnessed more than 22. 161 counties have been put under tornado warnings. 15 counties were tornado warned five or more times. The top-5 counties and their warnings were: Jackson County, MS with 12; Hancock County, MS with 11; Harrison County, MS with 11; Wayne County, MS with 11; and Greene County, MS with 9.

As of late September 4, at least 22 tornadoes have been confirmed (see details below). Surveys are still ongoing, and in many cases the information has not yet been posted. Filtered reports to the National Weather Service currently tally 42. Unlike many tornado outbreaks, official tornado reports to NWS are often close to or lower than actual tornadoes. As an an example, Katrina had almost double the tornadoes originally reported by the public or otherwise.

Below are day-by-day maps of select (any encompassed in the tornado warned areas) warnings from Isaac. Red indicates the tornado warnings. Following those maps, we’ll compile confirmations and other items as they come in.

This post will be updated as new information arises.

Sunday, August 26 2012 (500mb: 0z, 12z | IEM Local Storm Report App | SPC )