Hurricane-spawned tornadoes on radar

Thomas Loades

OK, I have a more pertinent question now. Is it possible for a hurricane-spawned tornado to have a TVS? While there was a tornado reported in NC during Charley, I checked on radar only to realize I had no idea what I was looking for . . . except I did see a suspicious feature that appeared as a green dot in a region of yellow–red reflectivities. The size of that dot was probably too big to be just the tornado — perhaps it (assuming it had to do with the tornado at all) was a temporary mesocyclone? Eventually it lost its circular shape and changed into more of a crescent shape — because of a mini-RFD?! (The crescent was pointing south! :? )[/i]
What you describe almost sounds like velocity folding. All radars, based upon their wavelength and pulse repetition frequency have a defined limit to what they measure. Once you cross over this threshold, the velocity immedietly switches over the the opposite extreme value. The result is you can get a large area of green/red and then inside you end up with the opposite value.

Just to add some background to this thread, there's a handful of papers from WFO's and academia which suggest spectrum width may be useful for identifying tornadoes in hurricane environments. I know at least one of them is online somewhere.

I believe the TDA algorithm has some problems in hurricane environments because the vortices are more transitory and the scales are smaller. Greg Stumpf might comment further if he sees this, as he has extensive experience with the TDA algorithm. If I'm not mistaken, DOW hurricane intercepts revealed some phenomenal stuff going on at the smallest scales.

I mentioned something to tha affect, but got a rebuttal from one of the NWS mets on this board -- may have been Bookbinder or Umsheid. Whatever the case, I thought they gave a couple of links for publications/etc... I'll search through the forums and see if I can find 'em...

Definitely wasn't me. While I find that spectrum width has little added value in normal supercells given the storm scale variability/turbulence in velocities, there is potentially significant added value using spectrum width in a hurricane where you're dealing with a more "smooth/laminar" flow so to speak, and interruptions like a tornado could show up fairly easily depending on the supercell characterstics and proximity to the central core. Most hurricane spawned tornadoes form in mini-supercells in the outer rainbands in the N and E quardrant. Tornadoes or meso-vorticies also form in the inner eyewall of intense hurricanes and can lead to significantly enhanced damage in small areas (this may have been the case yesterday).

If you remove the forward speed of the hurricane by using SRM instead of base velocity, I have found that "tornadic signatures" are much more easily identified. We identified some pretty heafty couplets ahead of both Bonnie and Charley, many of which produced tornadoes, and I was impressed by the lead times offered by the Florida NWS offices given how fast these vorticies move (often forward speeds of 50 to 70 mph).

More often than not, your ingredients for tornadogenesis in these rainbands are already present in the NE quadrant...enhanced low-level storm relative helicity and a warm/moist RFD. Therefore with sufficient instability present to support a rotating updraft (i.e. clearing between the rainbands), I've found that any storm usually able to reach 55-60dBZ, last for 30 minutes and reach a modest depth has a very good chance at producing a brief tornado.

Some links, that might be of interest.

Saint Louis University: The Tornadoes in Tropical Cyclones Group

Roger Edwards

NSSL SWAT Case Study - 12 July 1996 Hurricane Bertha-spawned Tornadoes


Must be more links out there, these are the ones I knew off hand.

Thanks for all that! I didn't realize a conventioal hook echo could still hold up in a hurricane — interesting that it does.