Tropical Storm Bertha Model Runs

[RL3AO]

Question.

Prob of RI for 25 kt RI threshold= 24% is 2.0 times the sample mean(12.3%)
Prob of RI for 30 kt RI threshold= 3% is 0.3 times the sample mean( 7.8%)
Prob of RI for 35 kt RI threshold= 1% is 0.3 times the sample mean( 4.5%)

Whats is/causes difference between those three? What does the 25/30/35kt mean?

[Chacor]

I'd always read that as "probability of 25-kt/30kt/35kt RI".

[brunota2003]

I think that is the amount increase. Chance of RI resulting in 25 knot increase in wind speed is 24%, whereas 30 knot increase is 3%.

I have been known to be wrong before, and probably am, but that is my guess.

[RL3AO]

Doesn't it seem wierd though that 25kt RI is 8 times more likely than 30kt RI? You would think those would be closed together since its only 5 more knots of stregthening.

[Chacor]

Not necessarily. At least, I don't find it weird. Perhaps there are factors the index detected that the model feels would not let Bertha strengthen more than a certain amount? I don't know.

[cycloneye]

I have the same question about that.Maybe a pro met can answer this.

[RL3AO]

Not necessarily. At least, I don't find it weird. Perhaps there are factors the index detected that the model feels would not let Bertha strengthen more than a certain amount? I don't know.

Must be. They were much closer together for Alma.

Prob of RI for 25 kt RI threshold= 76% is 6.1 times the sample mean(12.5%)
Prob of RI for 30 kt RI threshold= 55% is 6.6 times the sample mean( 8.3%)
Prob of RI for 35 kt RI threshold= 34% is 5.9 times the sample mean( 5.8%)

[Blown Away]

18z GFDL:
ATTENTION...NATIONAL HURRICANE CENTER
NCEP COUPLED GFDL HURRICANE MODEL FORECAST MADE FOR
TROPICAL STORM BERTHA 02L
INITIAL TIME 18Z JUL 3

FORECAST STORM POSITION

HOUR LATITUDE LONGITUDE HEADING/SPEED(KT)

0 13.3 25.1 285./ 9.9
6 13.8 26.5 289./14.4
12 13.9 28.0 274./14.3
18 14.3 29.4 288./14.7
24 15.3 31.0 301./18.6
30 15.9 33.2 286./21.9
36 16.1 35.2 275./19.1
42 16.3 37.2 276./18.9
48 16.5 39.1 276./19.0
54 16.9 40.9 280./17.4
60 17.4 42.8 285./18.7
66 18.1 44.9 290./21.1
72 18.8 46.6 292./18.2
78 19.5 48.0 298./14.6
84 20.4 49.3 304./15.2
90 21.3 50.3 311./12.9
96 22.0 51.2 308./11.1
102 22.8 51.7 326./ 8.7
108 23.8 52.4 328./11.6
114 24.8 52.9 332./11.3
120 25.6 53.6 322./10.1
126 26.4 53.9 339./ 8.0
[/b]

GFDL has Bertha moving almost 22kt in 24 hours, she is moving near 11kt rate now. Difficult to see such a rapid increase in forward speed in 24 hours. Bertha will have to pick up some serious speed to catch the weakness, IMO.

[Extremeweatherguy]

The 11pm NHC forecast track is pretty far north of the current model consensus (indicated by the grey line in the following image)...

https://my.sfwmd.gov/sfwmd/common/image ... orm_02.gif

[Derek Ortt]

they're actually close to the consensus

[RL3AO]

GFS is interesting

Weakness develops, moves Bertha NW. Weakness weakens , Bertha turns about due west (280?) at 17N.

Then is starts to move more NW around 72 hours.

[cycloneye]

Definitly the 00z GFS has shifted more west than the previous run.It has Bertha almost at 60w.

[RL3AO]

Bermuda might not be out of it yet.

[cycloneye]

It almost look like stalled in that area of 23n-57w.

[cycloneye]

Look at this now,It almost reaches 60w.Bermuda watch out.

[cycloneye]

OVER BERMUDA! But much weaker.

[RL3AO]

Thats a major shift. Lets see what the other models do and see if the GFS repeats in six hours.

[Ivanhater]

This trend is interesting..all models have been shifting and continue to do so..I suspect by tomorrow Bermuda will be in the path, then from there who knows...

[gatorcane]

well the westward shift is of no surprise. The weakness between the ridges as I pointed out earlier today is just so small and the GFS is deepening Bertha far too quickly. Still expecting models to shift left....

[NDG]

The reason why the GFS shifts westward beyond the 7 day range forecast is because it forecast, as the euro has been coming out with, for the weakness to lift out by day 5 or 6 and to make a left turn towards Bermuda before the GFS forecasts another weakness or trough to pick it up once again by day 11 or 12, between days 5 and 10 it only moves it just a couple hundred miles.
This is getting more and more interesting, and at the end we could see something very similar or a blend of the euro's and ukmet runs with the rest of the models.