Hurricane Irene Model and Forecast Discussion

[Midlo Snow Maker]

gfs coming in a little further SSW than 6z at hr 66

[Scott747]

Quick note on the 12z GFS that's currently running -

http://www.weather.g...d=ADM&node=KWNO

THE 12Z GFS HAS STARTED ON-TIME WITH THE FOLLOWING UPR AIR REPORTS AVBL FOR INGEST...14 ALASKAN...31 CANADIAN...76 CONUS...10 MEXICAN AND 11 CARIBBEAN...AS WELL AS 16 DROPSONDE AND 4 FLIGHT LEVEL RECON REPORTS FROM OVER THE CARIBBEAN SEA AND SOUTHWEST ATLANTIC OCEAN.

[Southland Wx]

Overall, GFS so far a couple hours slower and just a hair further west this run through 78 hrs.

[Southland Wx]

Also worth noting the GFS is substantially deeper with the trough coming across the Lakes on Friday night (10-15 dm lower heights). Not a surprise but...worth noting. Causing the shift to be to the right just a little compared to 00z now about 200 mi due S of HAT @ 96.

11PM Sat about 100 mi E of the NC/VA border 968 mb. No landfall.

Looks poised to hit LI or SNE extrapolating from the 120 hr...gotta go get lunch. In my own opinion, feel the GFS is overdoing the trough...I would probably not read terribly much into this and see if the Euro shows similar trends and how it compares to its 00z run last night.

Edit: Gloria redux this run.

[winterymix]

looks like no official landfall on outer banks this run.. just right

Agreed. It seems the huge Atlantic HIGH is retreating ever so slightly, allowing Irene to recurve just the slightest amount,

just enought to keep it offshore N. Carolina.

[yoda]

120 about 50 to 100 miles east of ACY 966 mb

[Ian]

typhoon tip should like this run... runs right into central long island at 132

[EasternUSWX]

Looks like any east shift halted for now. Still clipping NC and skirting coast.

[Riptide]

typhoon tip should like this run... runs right into central long island at 132

Irene landfalls with a central pressure of 972mb. The track is fooking weird, it bends around the Outer Banks and then heads north to impact Long Island.

[GD0815]

Irene landfalls with a central pressure of 972mb. The track is fooking weird, it bends around the Outer Banks and then heads north to impact Long Island.

Gloria....the only landfall hurricane I have ever been present for, pretty much followed that track.

[winterymix]

This looks like no landfall south of Long Island but amazing amounts of beach erosion.

[SP]

Gloria....the only landfall hurricane I have ever been present for, pretty much followed that track.

I was evacuated for Gloria......one heck of a tide.....they used a tug boat to keep the floating dock from floating away. Also forced them to add 5ft caps on the piling, post storm.

Crap, supposed to fly to Vegas Sunday!!

[WhiteoutMD]

JB says they sniff the water meaning they like to stay over water as long as they can

[Riptide]

Approaching the time frame where it's a good idea to consider the model tracks. Hard to say if there is a trend, just seems like alot of consistency from the GFS for a track just offshore w/landfall in the NE. Like the 0z GFS, there is still nothing to force it NE"ward after the second trough passes on the 12z GFS.

[stormitecture]

Question:

One thing with the models that I've kinda questioned (because I don't know, not because I think it's wrong) is the gradient spread and how it 'pushes' the gradient outward. I'm wondering if the model correctly places the pressure gradients and it's only the map (graphically) that shows this nice even spread with nice little circles, whereas reality seems to be different (where the pressure drops increase much more significantly toward the center).

[TUweathermanDD]

Approaching the time frame where it's a good idea to consider the model tracks. Hard to say if there is a trend, just seems like alot of consistency from the GFS for a track just offshore w/landfall in the NE. Like the 0z GFS, there is still nothing to force it NE"ward after the second trough passes on the 12z GFS.

To some extent I agree, though its encountering a bit of dry air which could weaken Irene and let her push west a bit longer. I'd also like to think that the GFS trended towards in ECMWF in the fact that it doesn't really recurve out to sea.

[Hugo]

this would be devastating for so many beaches / businesses and labor weekend follows

Worst winds shown on LI on the GFS are in the area of 50 kts.

The story would be rain and beach erosion, probably.

[SBUWX23]

Worst winds shown on LI on the GFS are in the area of 50 kts.

The story would be rain and beach erosion, probably.

50 kts is more than enough to do damage up here considering how much rain we could see if this track is right and with the amount of rain already seen this past month.

[Hugo]

50 kts is more than enough to do damage up here considering how much rain we could see if this track is right and with the amount of rain already seen this past month.

Yeah, there would be plenty of tree damage, roof damage, etc. Just saying that it wouldn't be Cat-3 devastation.

[Riptide]

I noticed that Irene's forward speed was slower on the 12z GFS. Perhaps the GFS is trending towards the Euro as ddweatherman proposed. This would cause the Northward deviation to occur earlier and result in a NC landfall. 12z euro will be enlightening.

[Paweatherguy1]

Worst winds shown on LI on the GFS are in the area of 50 kts.

The story would be rain and beach erosion, probably.

Could be wrong, but doesn't the GFS usually under do wind speeds in a tropical setting?

[Riptide]

Could be wrong, but doesn't the GFS usually under do wind speeds in a tropical setting?

The GFDL and HWRF are designed to predict tropical cyclone windspeeds at the surface.

[Paweatherguy1]

The GFDL and HWRF are designed to predict tropical cyclone windspeeds at the surface.

That is what I thought, so wouldn't it be more prudent when trying to look at wind speeds to look at those models rather than say "the GFS only has 50kt windspeeds." It seems you would be misusing the GFS if you are trying to gauge landfall wind speeds off of it?

[eyewall]

My discussion this morning: http://www.sandhillswx.com

[seabreezelou]

Quite right. Actually, if you were to go one step further, you would see that for anytime period prior to landfall on Long Island, the max speed out of the GFS is in the 60-65 kt range just south of NC. It's a synoptic scale model in a meso-scale situation, amongst other things, when was the last time you saw a 50kt wind on the GFS? Similarly, the Euro only has speeds up to 55-60kts around NC, 40-45 nearest to Long Island.

That is what I thought, so wouldn't it be more prudent when trying to look at wind speeds to look at those models rather than say "the GFS only has 50kt windspeeds." It seems you would be misusing the GFS if you are trying to gauge landfall wind speeds off of it?

[Cheeznado]

12Z CMC very similar to the GFS- brushes NC Outer banks, then up towards eastern LI

[Paweatherguy1]

Quite right. Actually, if you were to go one step further, you would see that for anytime period prior to landfall on Long Island, the max speed out of the GFS is in the 60-65 kt range just south of NC. It's a synoptic scale model in a meso-scale situation, amongst other things, when was the last time you saw a 50kt wind on the GFS? Similarly, the Euro only has speeds up to 55-60kts around NC, 40-45 nearest to Long Island.

Is there a way to extrapolate then.....most seem to think that 100 kts around NC is likely...does that mean that if it is showing 50 kts up in NE, that we would be look at 80-90 kts up that way, with a cat 2 storm?

[lsukev]

The fact that Irene hugs the coast after making the turn is odd to me. All it will take is a broader turn and it's going to be a windy weekend along I-95.

[Typhoon Tip]

Wow if this is not a dicey ...super high risk scenario for the I-95 corridor nothing is! Considering that by D4 the average NHC forecast error is 200 mi, 250 by D5, the implicaitons range from almost no impact, to who-knows-what...

The speed of this thing limits the "slam" in scenario. One thing to note, for New England (and NS for that matter), the shelf waters are typically ineffectual at weakening the systems substantially enough because they are moving so fast; in this case, this 24 hours to move from the latitude of Cape H to LI is too long.... That means it will spend a minimum of 8 hours over the shelf waters tucked in NW of the Gulf Stream, and that should impose a weakening - how much so is uncertain, BECAUSE, the water in the shelf region is in the mid to upper 70s. The thermocline is shallow there, so it wouldn't take long to upwell, but it is a little worrisome that a TC moving N paralleling the EC toward LI might not be impeded as much as one normally would. This last 2 weeks of any given August are like that - you really get most of these up there in September, when the apex SSTs are by the board and probably there has already been a NW synoptic flow event to turn over the summer waters. That has not happened yet so a typical translation over the shelf does carry a little bit of uncertainty as to how much mitigation would be imposed.

That said, obviously SC/NC/DE/NJ/NYC are all on the table in this poker game right now and no hands have been callled... Although, SC is sweating and everyone at the table knows it.

[Ed Lizard]

Wow if this is not a dicey ...super high risk scenario for the I-95 corridor nothing is! Considering that by D4 the average NHC forecast error is 200 mi, 250 by D5, the implicaitons range from almost no impact, to who-knows-what...

The speed of this thing limits the "slam" in scenario. One thing to note, for New England (and NS for that matter), the shelf waters are typically ineffectual at weakening the systems substantially enough because they are moving so fast; in this case, this 24 hours to move from the latitude of Cape H to LI is too long.... That means it will spend a minimum of 8 hours over the shelf waters tucked in NW of the Gulf Stream, and that should impose a weakening - how much so is uncertain, BECAUSE, the water in the shelf region is in the mid to upper 70s. The thermocline is shallow there, so it wouldn't take long to upwell, but it is a little worrisome that a TC moving N paralleling the EC toward LI might not be impeded as much as one normally would. This last 2 weeks of any given August are like that - you really get most of these up there in September, when the apex SSTs are by the board and probably there has already been a NW synoptic flow event to turn over the summer waters. That has not happened yet so a typical translation over the shelf does carry a little bit of uncertainty as to how much mitigation would be imposed.

That said, obviously SC/NC/DE/NJ/NYC are all on the table in this poker game right now and no hands have been callled... Although, SC is sweating and everyone at the table knows it.

May be straw grapsing, but I would hope East winds ahead of Irene might actually induce a net Southeast flow or warmer water from the jet Gulf stream, figuring the water would bend somewhat right of wind gradient due to Coriolis affect.