STORM TRACK: March 31, 1984 (Volume 7 Issue 3)

Barbara (Looking for Typhoons) White writes from Guam that, "the little NOAA weather observatory here doesn't have satellite imagery or upper air data ... but does have all the advisories that are issued for every tropical cyclone." The Naval air base has the rest of this, but access is restricted. Otherwise, there are some stateside amenities such as satellite TV and 13 channel cable to date, with more on the way. "I'm looking forward to Tim Marshall's account of Alicia. It is always interesting to hear different views of the same storm" (Read on Barbara).

Howie "Cb" Bluestein, Oklahoma University professor and a research chase-director, writes that he plans to launch portable radiosondes into storms this spring, with support from NSSL and OU. He hopes to get some good soundings from and near wall clouds and from adjacent storm environments, including inflow regions, rear flank downdrafts and along and just east of dry lines, just before deep convection begins. The tentative plan is to launch from the photo site or enroute (dry line intersects), as appropriate.

...end of the chase.

Hey! Tim Marshall has come up with a "real time" way to estimate the F-scale intensity of tornadoes. For neophyte storm buffs, the "F-soale" is a subjective measure of estimated wind speed, developed by Dr. Ted Fujita at the University of Chicago. It ranges from FO (weakest) to F$ (strongest) and is normally based on after-the-fact storm surveys of structural damage. F0 winds are 40-72 MPH, Fl = 73-112 MPH, F2 = 113-157 MPH, F3 = 158-206 MPH, F4 = 207-260 MPH, and F5 = 261-318 MPH. Space doesn't permit a complete list of damage descriptors, but most destructive tornadoes are in the Fl - F2 range, which means that roof surfaces are peeled and mobile homes overturned (F1) or roofs are torn off frame homes and mobile homes are demolished (F2). At F3, some walls are torn off well-constructed houses, heavy cars are lifted off the ground and thrown, and trains are overturned.

Tim believes that the size and shape of a tornado vortex "are not, reliable indicators. However, I thought of another method. If you're close enough to the base to see the dust motion and subvortex or cloud tags, then its possible to visually track these as they rotate around the tornado. By using simple geometry, a crude yet basic method can be used to obtain an F-scale rating.

If you assume that the flow is rotating circularly and have a good idea on the tornado's diameter, then a method of 'visual photogrammetry' can be used. The circumference of a circle is F times the diameter D. The length of a half revolution is pi x D/2. If you watch a subvortex (for example) move a half revolution and document the time, you can figure this for yourself as follows, or use the attached table to get the F-scale intensity."

Thanks, Tim, for a lot of work and a very interesting letter!

Marty Feely, from California, suggests an alternative chase idea for frustrated (or satiated) chasers: photographic pursuit of a near total eclipse of the sun on May 30. This is "an Annular eclipse; one in which the moon is too far away from Earth to cover the sun completely. Along a narrow path across the southeastern U.S. the moon will block all but an extremely thin ring around the outer edge of the sun. This particular eclipse is very rare. So close is it to being total, that within a five mile wide path of annularity, extending from near New Orleans to near Washington, D.C. -- the ring may not be complete! The moon's shadow (maximum eclipse) will enter Louisiana southwest of New Orleans a few minutes after 11 AM CDT. Twenty minutes later, it will pass directly over Atlanta, Georgia (12:22 EDT). The path also skirts Greenville, South Carolina and Greensboro, North Carolina. It then passes just south of Richmond, Virginia and out into the Atlantic Ocean, east of Washington, D.C. at 12:50 EDT. I plan to travel to the path of annularity (wherever weather conditions are most favorable). If any chasers would like to join me on this different sort of chase, contact Marty Feely at 401 North Base Avenue, Norman, Oklahoma 73069 after April l. But wherever you are on May 30, be prepared for darkness at noon! Of course, don't look directly at the sun, since it will not be completely covered at any point. Use traditional indirect observation methods, such as pin-hole projection or specially coated lenses."