So it turns out the storm that kicked off a microburst in Pinellas Park, spun up some pretty strong low level rotation over downtown St Pete then moved south, actually produced an eF-1 Tornado just east of Sarasota! The NWS recently conducted a damage survey of a plant farm with several metal buildings and dozens of greenhouses that were completely destroyed or badly damaged.
The very unfortunate thing I would like to point out here is that this single storm was not severe storm warned or tornado warned at any point in its life cycle which unfortunately may cast a negative light on the hard working folks at the NWS office in Ruskin. I grabbed some archived level 2 radar data from the NCDC and I would like to show you radar snapshots of what forecasters at the NWS would have seen as this storm was unfolding. You can click any of these for full size.
A little background on the day’s forecast first. The area was under a severe thunderstorm watch which had just expired at 9pm. The severe thunderstorm watch notated an elevated risk for an isolated waterspout or tornado to develop along boundary collisions. The day had already brought severe storms widespread across the state, with CAPE values at or around 4000 J/KG. Excerpt from the watch’s discussion quoted below:
SEASONABLY STRONG NLY FLOW ALOFT WILL CONTINUE ACROSS
FL THIS AFTERNOON/EVENING AS DEEP MID LEVEL TROUGH DIGS OFF THE NERN
FL COAST. AIR MASS REMAINS VERY UNSTABLE…DESPITE EARLIER LINEAR
MCS…WITH SUFFICIENT SHEAR FOR ORGANIZATION INTO LINES/CLUSTERS AND
PERHAPS A BRIEF SUPERCELL OR TWO. DAMAGING WINDS AND ISOLATED LARGE
HAIL WILL REMAIN PRIMARY THREATS…ALTHOUGH A BRIEF
WATERSPOUT/TORNADO COULD ACCOMPANY STORMS ALONG RESIDUAL SURFACE
BOUNDARIES.
Now with this information in mind, I would be particularly mindful of any rapidly developing low level rotations. Florida tends to not get strong tornadoes, but those we do get form very rapidly and can be hard to detect, generally along strong boundary collisions from multiple thunderstorms. The below summary is an excellent example of this situation. The summary begins below:
06/23/09 9:58pm EDT – This is how the storms began. Note the large cluster of thunderstorms east and southeast of Tampa Bay. These generated an outflow boundary which shows up on the radar very well (thin line of reflectivity from about Parrish through upper Tampa Bay into Tarpon Springs). This boundary was moving very slowly to the west over Tampa Bay. Overall storm motion for the day is to the south-southeast. Another outflow boundary not visible to radar is moving south near New Port Richy. This boundary collision is kicking off new storms near New Port Richy and just offshore in the gulf.
06/23/09 10:29pm EDT – Storms continue to grow larger along the two intersecting outflow boundaries. Gusty winds around 27 knots show up on doppler radar near New Port Richy. Overall storm motion is to the south-southeast.
06/23/09 10:59pm EDT – At this time the storms are very strong, borderline severe. Radar indicates 0.77 inch hail near Anclote Key and into Dunedin with wind gusts to 37 knots in this same area. The leading edge of this storm’s reflectivity now begins to indicate the location of the southerly moving outflow boundary. Note the storm and the westerly moving outflow boundary are now colliding over Pinellas Park. Additionally there apears to be a very small area of possible rotation over Clearwater, however this is the only volume scan this feature appeared in.
06/23/09 11:15pm EDT – This is the aproximate start time of the microburst damage in Pinellas Park. What we see here is the southward moving outflow with strong storm development to its north, colliding with the now stalled out westerly outflow boundary. Radar indicates 0.93 inch hail near Feather Sound and the Gandy area. Additionally radar velocity now shows 50 knot winds in Highpoint, just west of St. Pete Clearwater Intl Airport. 50 knots is the baseline for a storm to be considered severe. At this time it would have been appropriate to issue the severe storm warning considering the hail size and wind speeds indicated by radar met severe criteria. Additionally the environment was still forecast to be favorable for producing severe weather, so this storm was likely to only intensify.
06/23/09 11:19pm EDT – This is the time the microburst likely hit Pinellas Park. You can see the leading edge of the storm had just passed to its south. Additionally I remember looking at this storm live as it was moving through and noticing this scan appeared to have an inflow region right over I-275 and 62nd Ave N, the area impacted by the microburst. The velocity scan shows outbound velocity in this area, paired with very strong inbound just to its west, this is the area where the two outflow boundaries were colliding. Note the radar indicates 0.89 inch hail over old northeast St. Pete, and the southerly moving outflow is now visible on the velocity scan.
06/23/09 11:25pm EDT – The next radar volume scan, note the storm has a very well defined Weak Echo Region (WER) just north of St Petersburg. This indicates an area of strong inflow to the storm, with very gusty winds. The velocity scan confirms the outbound winds flowing into this area. Strong inbound winds are indicated by the green color in downtown St Petersburg. Radar indicates 0.65 inch hail in this area.
06/23/09 11:30pm EDT – This is a zoomed out version of a radar snap I took and posted on a previous blog entry. This shows very well pronounced low level rotation over downtown St Petersburg. The reflectivity plot on the left shows a classic hook echo, and the velocity plot on the right shows a inbound/outbound couplet which existed in radar volume scans all the way up through 8000 feet! While no confirmed tornado formed from this, I would have strongly considered issuing a tornado warning at this point. Considering the day’s forecast and all available information at the time, this storm appeared ready to produce a tornado at any time. I will re-post the zoomed in version of this radar snap below:
In this zoomed in version, you can clearly see the Weak Echo Region (WER) on the left, with the precipitation wrap around forming the hook echo shape. On the right, you can see a velocity couplet very well defined. Again if I were watching this storm unfolding live, I would consider this storm to be producing a tornado or at least very strong winds. This is actually something which validated as a reader of my site who lives in Coquina Key confirmed damage in her neighborhood from this event! Quote listed below:
We live on Coquina Key and experienced quite a bit of damagage. It was very localized and could have been some sort of tornado. The noise I heard just before the storm broke was the scaries thing I’ve heard.
06/23/09 11:35pm EDT – The strongest winds with the storm have moved off into the middle of Tampa Bay at this time, though low level rotation still appears to be present. Approximately 10,000 power outages are reported around this time from the strong winds including around Treasure Island.
06/23/09 11:45pm EDT – The storm now moves into Manatee County, over Port Manatee first. Emergency Management reports a funnel cloud visible around11:49pm, only 4 minutes after this radar scan. Considering the current radar and velocity plots, it is likely to of occurred closer to 11:45pm and been 4 minutes delayed in reporting, though that’s just an assumption. No well defined rotation shows on this velocity plot, but at the very least you can see areas of strong winds moving ashore near Port Manatee.
6/24/09 12:15am EDT – This is just 6 minutes before the storm moved across Fruitville Road and produced the eF-1 tornado. You can see the intense winds and possible rotation right along the Sarasota and Manatee county lines. Outbound winds are reaching 64 knots and inbound winds show 4 knots. 68 knots of shear in this area, this would be capable of producing a weak tornado.
06/24/09 12:21pm EDT – This is taken as the storm passes over Fruitville Road to the east of Sarasota. This is likely the time that the tornado began to develop, though radar velocities do not show a very compact circulation in this area. You can see an area on the reflectivity that vaguely resembles a hook, though it is not a very well pronounced one. There is also another area to its east that does have some gate to gate shearing. This is likely the area that the tornado began to develop.
06/24/09 12:25pm EDT – This is just a minute before the tornado passed over Fruitville Road and into the Plant Farm. You can see a very small area of shearing winds occuring just southwest of Verna. The highest winds in this area are 66 knots outbound, which equals 75mph. The Plant Farm impacted by this is immediately south of this area of red/green color. Fruitville Road is the pink road traveling west to east across the middle of this image.
The storm gusted out after this point and lost its severity. Again, this storm should have been severe warned back at 11:15pm, and possibly even tornado warned at 11:30pm. Thankfully nobody was hurt during these events (as far as I know). Unfortunately this storm had the potential to be tornado warned up to 55 minutes in advance when the first signs of strong rotation were detected, before the tornado near Sarasota touched town. At the very least this storm should probably have been severe warned as there were numerous volume scans indicating wind speeds exceeding severe criteria.
Below are a few damage pictures taken by the NWS. These are pictures around the Plant Farm east of Sarasota.
Link to the NWS’s full damage survey is located below:
http://www.srh.noaa.gov/images/tbw/TopNews/TornadoHitsPlantFarm.htm
Location of the tornado damage noted on the google map below:
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