TD10 / TD12 (2005)

[Ed Schoenborn]

Many times I have seen tropical depressions degenerate and several days later regenerate with the same td number yet when TD10 degenerated it was renumbered TD12 when it regenerated. I have never heard a satisfactory answer as to why it was renumbered TD12 instead of retaining the number TD10. Why was it renumbered? Ed

 

[rdale]

NHC makes it pretty clear that since 10's circulation was completely dead, it was only appropriate to rename. Read the Katrina report at http://www.nhc.noaa.gov/2005atlan.shtml

 

[Ed Schoenborn]

Since I use webtv instead of a computer I was unable to gain access to the Katrina report mentioned above.

 

[rdale]

a. Synoptic History
The complex genesis of Katrina involved the interaction of a tropical wave, the middle tropospheric remnants of Tropical Depression Ten, and an upper tropospheric trough. This trough, located over the western Atlantic and the Bahamas, produced strong westerly shear across Tropical Depression Ten, causing it to degenerate on 14 August approximately 825 n mi east of Barbados. The low-level circulation gradually weakened while continuing westward, and it eventually dissipated on 21 August in the vicinity of Cuba. Meanwhile, a middle tropospheric circulation originating from Tropical Depression Ten lagged behind and passed north of the Leeward Islands on 18-19 August. A tropical wave, which departed the west coast of Africa on 11 August, moved through the Leeward Islands and merged with the middle tropospheric remnants of Tropical Depression Ten on 19 August and produced a large area of showers and thunderstorms north of Puerto Rico. This activity continued to move slowly northwestward, passing north of Hispaniola and then consolidating just east of the Turks and Caicos during the afternoon of 22 August. Dvorak satellite classifications from the Tropical Analysis and Forecast Branch (TAFB) of the Tropical Prediction Center (TPC) began at 1800 UTC that day. The upper tropospheric trough weakened as it moved westward toward Florida, and the shear relaxed enough to allow the system to develop into a tropical depression by 1800 UTC 23 August over the southeastern Bahamas about 175 n mi southeast of Nassau. The depression was designated Tropical Depression Twelve rather than “Ten” because a separate tropical wave appeared to be partially responsible for the cyclogenesis, and, more importantly, the low-level circulation of Tropical Depression Ten was clearly not involved.

 

[Pat Lawrence]

Didn't read all of the words in this thread, but at the time I think there was a question regarding a remnant mid-level circulation. Didn't make much difference regarding naming etc. anyway.

Pat

 

[rdale]

If you don't want to read the whole thing, all you need to answer your question is to read the last sentence. I'm not sure what you mean about the mid-level circulation.

 

[Pat Lawrence]

THE NWS RULES GOVERNING THE NAMING OF TROPICAL CYCLONES SPECIFY THAT...WITHIN A BASIN...WHEN A CYCLONE FORMS FROM THE REMNANT OF A PREVIOUSLY EXISTING CYCLONE...THE OLD NAME/NUMBER IS RETAINED.
TROPICAL DEPRESSION TWELVE HAS A COMPLEX GENESIS THAT LIKELY INCLUDES A MID-LEVEL REMNANT OF FORMER TROPICAL DEPRESSION TEN. A REVIEW OF SATELLITE AND RAWINSONDE DATA OVER THE PAST WEEK OR SO SUGGESTS THAT A SECOND DISTURBANCE APPROACHED AND COMBINED WITH THE MID-LEVEL REMNANT OF TROPICAL DEPRESSION TEN ON 20 AUGUST. BECAUSE IT IS IMPOSSIBLE TO DETERMINE WHICH OF THESE TWO SYSTEMS IS ASSOCIATED WITH TODAY'S GENESIS...WE HAVE ELECTED TO USE THE DESIGNATION TWELVE RATHER THAN TEN FOR THE NEW DEPRESSION. THIS SITUATION DIFFERS FROM LAST YEAR'S REGENERATION OF IVAN...IN WHICH THE LOW-LEVEL REMNANT OF THAT SYSTEM REMAINED A DISTINCT FEATURE THAT COULD BE FOLLOWED CONTINUOUSLY UNTIL IT REGENERATED.

Words from Stacy Stewart at NHC from last year... like I said at the time this may have been the thinking... doesn't mean thinking can't change does it?

Pat

 

[rdale]

Doesn't look like anything changed - they used a new number last year, and upon final review after the season ended still thought it was appropriate to use a new number.

 

[Pat Lawrence]

You asked about the mid-level remnant (I'll read the Hurricanes Center's summary later)...... that was explained. At least I'm assuming that's what you meant when you said you weren't sure what I meant by a mid-level remnant.

Like I said earlier, it would have been the K storm last year whether it was called TD10 or TD12.