Capstone: Hurricane Ivan, 15 to 16 September 2004

The event

Ivan came ashore near the Alabama and Florida line early on 16 September 2004. The tornado outbreak in its rainbands had already begun the day before and ran across the south-east.

Two of those deaths and much of the damage in this office's area came from a pair of F2s on 15 September: Panama City Beach in Bay County, one death and seven injuries, and Blountstown in Calhoun County, four deaths and one injury. The Tallahassee forecast area counted 24 tornadoes in all: 14 F0, 8 F1 and 2 F2.

A note on the count, because you will meet a different one: NCDC catalogues the wider continuous outbreak at 120 tornadoes, passing Hurricane Beulah's 1967 record of 117. This lesson uses the NWS and AMS figure of approximately 117 throughout so the numbers here agree with each other. Both are real counts of slightly different things.

What the office was working with

This is the part worth studying. NWS Tallahassee monitored more than fifty identified mesocyclones over the event and issued 130 tornado warnings.

Why nobody could see anything

Every difficulty from lesson 8 was present at once. The storms were mini-supercellsA supercell with a shallower, smaller and weaker rotating updraft than a classic one, typical of tropical cyclone rainbands. Produces tornadoes in an environment with a fraction of the instability a Plains supercell needs. in tropical rainbands with shallow, small circulations. They were rain-wrapped. Much of the activity ran through the night. And the whole region was already inside a landfalling hurricane, so the conventional advice to find a safe vantage with a clear view to the south-west was not available to anybody.

A spotter's value in that event was not in confirming funnels. It was in damage reports, timings and locations after the fact, which is what turned 20 of those 130 warnings into verified events and left a record precise enough that we can read the office's performance twenty years later.

What a report needed to carry

The WHEN clause is the one that decides whether a report verifies a warning. A damage report timed to when you called it in rather than when the damage happened can fall outside the warning polygonThe shape a warning is drawn on, replacing whole-county warnings in 2007. Being inside the shape is what matters, not which county you are in.'s valid window and verify nothing. In a nocturnal, rain-wrapped outbreak where after-the-fact damage reports are most of the ground truth available, that detail is doing more work than any funnel identification.