ATL: Ex-Tropical Storm GASTON - Discussion

[Stratosphere747]

FWIW

The LGEM has handled Gaston very poorly to this point. I would take what it is currently showing with the ol grain of salt. Going back a few days gives a indication of how bad it has been. Still one of the better intensity models but not so far with Gaston.

[ColinDelia]

are those intensity models based on showing potential if things are just right or do they represent that things are expected to get just right? hope you get what iam asking.

They represent what is expected.

Let me go over SHIPS because it is the easier to understand. Here is the basic idea. SHIPS is a statistical method where a number of factors are considered.
For every period each factor is either a windspeed addition or subtraction and the numbers (in knots) are added together for all the factors each period. The numbers for each factor come from the historical relationships between those values and whether storms typically strengthened or weakened at those values and to what degree.

So a high ocean temperature will add x knots to the top wind speed depending on the temperature if it is above a certain value; the higher the temp. teh higher the gain in knots. The largest factors are shear and ocean temperature. When there is high shear expected SHIPS subtracts something from the top wind speed in that period depending on what the historical correlation is.

Every few years new correlations for recent storms are computed and new values obtained.

In the next 5 days, SHIPS adds 41 knots to Gaston's top wind speed for the ocean temperatures along its expected path.
17 knots are added for the vertical shear magnitude. 13 knots are added for what a storm would normally gain at this time of year.
11 knots are added for the ocean heat content. 7 knots are added for the vertical shear direction. There are a number of smaller factors
also.

While there are certainly shortcomings the statistical methods have been the most accurate of the models for intensity forecasts with LGEM being the best the past 3 years. DeMaria, one of the creators of SHIPS is the creator of LGEM.

You can get further info from DeMaria et al's papers.
SHIPS
http://rammb.cira.colostate.edu/researc ... _SHIPS.pdf
http://rammb.cira.colostate.edu/resourc ... eMaria.pdf

LGEM
http://rammb.cira.colostate.edu/resourc ... lified.pdf

[Migle]

I am guessing where going to see Code Orange on this one at 8. It finally has some convection to it, something we haven't seen alot of in Ex-Gaston's life. I still think Bailey is going to be make a donation though

[tolakram]

It's heading directly for the mountains, I don't see how this thing stands a chance, even if it is wrapping up again. Looks like it will be yet another heavy rainmaker for Haiti and the DR, unfortunately.

[Steve]

Had a chance to look at the models, and there is very, very little support (= about none at all). Best I could tell with NOGAPS, the remnants hook up with a heat low off of South America and close something off near Central America/Yucatan. Doesn't seem too likely at this point that anything "real" (= not exactly Cat 4) is going to come from the Remnants. But the SW motion that was predicted has been on with XTRP all day as the remains must be going SW or WSW for that to continue to point equatorial. I don't know, I'm not tracking the circulation or whatever it is they're tracking. But I'm still mildly interested.

[tolakram]

Live loop: http://wwwghcc.msfc.nasa.gov/cgi-bin/ge ... mframes=25

[ColinDelia]

The LGEM has handled Gaston very poorly to this point. I would take what it is currently showing with the ol grain of salt. Going back a few days gives a indication of how bad it has been. Still one of the better intensity models but not so far with Gaston.

Very true. The model sample for SHIPS includes named tropical cyclones only. So anything before a storm reaches TS status should probably be taken with that grain of salt. The error for pre-depression storms must be HUGE as many of them don't even form.

[Bailey1777]

thank you colin i love when yyou get infomative answers to questions and let me say i have read many of your post and you bring alot to the storm2k family..

[Shuriken]

Bailey, the intensity models are based on the forecasted conditions in the next few days.
Remember, the LGEM is a reliable intensity model and is not one to go bonkers with every storm. Great potential is there.
It either dissipates, or explodes imo.

Exactly...and some of them do both -- Hurricane Iris being an example of that: A healthy-looking TD in the central Atlantic completely pukes into an open wave while crossing the islands (and by "completely" I mean just that; there wasn't the least hint of rotation left, just a few cu along an advancing line)...and a few days later is a 145mph storm pummeling Belize.

Storms in the Caribbean are doing one of two things: (a) dying, (b) exploding.

[KWT]

I'd still be surprised if anything comes from this just yet but I'd imagine in the W.Cairbbean things will be a little more productive for the development of a system and if it can get into the BoC/Gulf then it'll deffo need watching without any doubt at all...

It does look better now but we've been here before in the last few days...

[Aric Dunn]

I'd still be surprised if anything comes from this just yet but I'd imagine in the W.Cairbbean things will be a little more productive for the development of a system and if it can get into the BoC/Gulf then it'll deffo need watching without any doubt at all...

It does look better now but we've been here before in the last few days...

yeah its not happening tonight or anything.. but likely more towards central/western carrib

[fci]

The LGEM has handled Gaston very poorly to this point. I would take what it is currently showing with the ol grain of salt. Going back a few days gives a indication of how bad it has been. Still one of the better intensity models but not so far with Gaston.

Very true. The model sample for SHIPS includes named tropical cyclones only. So anything before a storm reaches TS status should probably be taken with that grain of salt. The error for pre-depression storms must be HUGE as many of them don't even form.

That's a great point. Pre-depression SHIPS seems to take most up to high wind speeds and I remember being told to ignore it by Pro Mets. I understand why now due its inputs being tropical cyclones only. Thanks for the explanation

[Bailey1777]

i see our nightly cloud top warming is taking place.

[Sanibel]

It could poof from drawing cold air over the mountains of Hispaniola which then allows the shear (or weak conditions rather) to gain the upper hand. In this case it would make the development callers look foolish. But the system is curling up IMO.

[Bailey1777]

if it is now a wave vs. a closed low wouldn't that help lessen the effects the mountains may have on it?

[Bailey1777]

seeing something new tonight new cold tops forming.....maybe.....

[CalmBeforeStorm]

http://www.ssd.noaa.gov/goes/east/carb/flash-wv.html

I'm really not sure if Gaston will ever regenerate but have you noticed the significant northern progress he is making? The system seems like it is being influenced by the upper level low ahead of it and has kicked significantly north of west. I wouldn't be at all surprised to see it above the eastern tip of Cuba at some point.

[Bailey1777]

to elaborate the last several days as night approached t.s. activity would die off but tonight as t.s.'s relaxed a new burst just occured. maybe a sign we'll see. as far as movement still seems pretty much west to me.

[expat2carib]

It's the first year the NHC TWO works with a percentage of development within 48 hours.

It would be great to have a quality test on these percentages.

If they forecast a wave to become a TC within 48 hours and give it 70% and it doesn't become a TC within 48 hours they were 70% wrong and 30 % right.

If they forecast a wave to become a TC within 48 hours and give it 30% and it becomes a TC within this margin they were 70% wrong and 30% right.

Would be nice to have those figures. The NHC gave their TWO'' something quantitative. And quantity can be reality tested.

What's the percentage they were wrong and what's the percentage they were right?

How much they were wrong on X-Gaston?

[Ivanhater]

New burst near the center