Verification of tracks made on Nate (2017) using GEFS mean fields

August 16, 2019

This is a repost from early 2018

I made 21 tracks about Hurricane Nate. Additionally, there was one case, where I missed cyclogenesis. Forecast for peak intensity varied much between tracks, but generally it was with better skill than climatology. Position errors evolved over time. First, it was not certain at all, whether Nate will move north from Caribbean. At the same time, time and position of cyclogenesis was very variable. When eventually tracks began consistently showing a move to north, there was typically a rather abrupt turn to left. The actual record-breaking forward speed of Nate in the Gulf of Mexico was apparent only in last few tracks.

My intensity analysis begin at September 29, 06Z, which is the earliest time, at which some of my tracks had cyclogenesis. Position analysis begins at first time with best track data, October 2, 18Z. Position analysis ends at last time with best track data, October 8, 12Z. Intensity analysis ends at October 17, 06Z, after which none of my tracks continued.

Since I give only SSHS categories in my tracks, I don't calculate intensity errors in units of speed, but in categories. For this purpose, I define tropical storms as "Category 0", tropical depressions as "Category -1" and non-existence of a tropical cyclone as "Category -2".

I compare intensities only in cases, when either the best track data or my track has a tropical cyclone, or both. In other words, I leave the comparison out of calculations, if both best track data and my track lack a tropical cyclone.

In the 21 tracks, formation times ranged between September 29, 06Z and October 8, 18Z. Median was October 6, 12Z and average was October 5, 14Z.

The 22 peak intensities (the complete miss included) ranged between non-formation (Category -2) and Category 5. Median was Category 2 and average was Category 1.8.

Dissipation times ranged between September 30, 18Z and October 17, 12Z. Median was October 11, 12Z and average was October 11, 11Z.

The following lines will have the format:

lead time ... number of true detections ... number of misses ... number of false detections ... number of position comparisons ... number of intensity comparisons ... average error in intensity category ... bias in intensity category ... average error in latitude ... bias in latitude ... average error in longitude ... bias in longitude ... upper limit for scalar error in position (nautical miles)... calculated scalar bias in position (nautical miles)

168h ... 2 ... 2 ... 2 ... 2 ... 6 ... 2.0 ... +0.3 ... 10.9 ... 10.9S ... 1.6 ... 1.6E ... 660 ... 660
192h ... 0 ... 4 ... 4 ... 0 ... 8 ... 2.3 ... +0.3 ... N/A ... N/A ... N/A ... N/A ... N/A ... N/A
216h ... 0 ... 6 ... 2 ... 0 ... 8 ... 2.4 ... -0.6 ... N/A ... N/A ... N/A ... N/A ... N/A ... N/A
240h ... 2 ... 5 ... 3 ... 2 ... 10 ... 1.8 ... -0.2 ... 5.0 ... 4.1S ... 5.7 ... 5.7E ... 440 ... 410
264h ... 4 ... 2 ... 4 ... 4 ... 10 ... 1.5 ... -0.1 ... 4.1 ... 4.1S ... 5.2 ... 5.2E... 390 ... 390
288h ... 4 ... 1 ... 6 ... 5 ... 11 ... 1.7 ... +0.8 ... 6.3 ... 5.9S ... 5.4 ... 5.4E ... 490 ... 470
312h ... 3 ... 2 ... 9 ... 4 ... 14 ... 1.5 ... +0.9 ... 5.9 ... 4.9S ... 5.0 ... 4.2E ... 460 ... 380
336h ... 3 ... 1 ... 9 ... 3 ... 13 ... 2.0 ... +1.7 ... 1.3 ... 1.3S ... 2.6 ... 2.6W ... 170 ... 170
360h ... 3 ... 1 ... 6 ... 3 ... 10 ... 2.3 ... +1.7 ... 4.7 ... 4.7S ... 3.5 ... 3.5W ... 350 ... 350
384h ... 3 ... 1 ... 6 ... 3 ... 10 ... 1.7 ... +0.9 ... 10.3 ... 10.3S ... 5.6 ... 5.6W ... 700 ... 700
408h ... 2 ... 0 ... 4 ... 2 ... 6 ... 2.3 ... +2.0 ... 15.4 ... 15.4S ... 7.3 ... 7.3E ... 1020 ... 1020
432h ... 1 ... 0 ... 4 ... 1 ... 5 ... 3.0 ... +3.0 ... 18.3 ... 18.3S ... 7.6 ... 7.6E ... 1190 ... 1190
456h ... 0 ... 2 ... 5 ... 0 ... 7 ... 3.4 ... +2.6 ... N/A ... N/A ... N/A ... N/A ... N/A ... N/A
480h ... 0 ... 2 ... 5 ... 1 ...7 ... 3.3 ... +2.1 ... 5.8 ... 5.8N ... 0.6 ... 0.6W ... 350 ... 350

Here are the tracks once again.

September 13, 06Z run: