ATL: IRMA - Post-Tropical - Discussion

[MississippiWx]

Now is as good a time as any to remind everyone that the Day 5 location of Irma from the NHC is still a little over 100 miles from even reaching the Lesser Antilles. A tropical cyclone will be within the 5-day cone 60-70% of the time. The average track error at that distance in time can be hundreds of miles. Notice, I haven't even mentioned anything 7+ days away which is how long it would take to even be close to the Bahamas/US.

Also, 4-5 days before Harvey devastated Texas, we thought it would be a Category 1 hurricane or less into Central Mexico.

Always stay prepared and abreast. September is traditionally a bad month for hurricane landfalls in active years.

[Aric Dunn]

IR Showing a much larger eye beginning to show still ragged though but wont be but a few more hours till the ERC is complete.

https://weather.msfc.nasa.gov/goes/abi/ ... and14.html

IR channel 4 or 7 or 9 lol

[nativefloridian]

The NHC discussion has mentioned their southern bias the past few advisories, but I'll guess they will steer away from that very soon, and that will put the forecast track outside the area.

The forecasters base a lot on persistence, and Irma has been very persistent to the WNW and the reason the models are trending right, versus yesterday's more southern route...

Frank

I dont think they are going to change their thinking much. they know that tracks and set ups like this typically lead to longer more prononced westerly motion after the wsw to sw dive. There are a number of physical atributes that point to a southern route. Also dont forget that as this systems bottoms out of the sw dive it will be hitting peak intensity and likely will be pumping of that ridge to its north somewhat and models do not do well with that. It is still quite likely we see a shift south in models the next few runs expecially once it begins that turn to the WSW to SW.

Aric, could you please advise if I'm correct to assume that when you say "pumping of that ridge" that it means the storm could aid in intensifying or increasing the size of the ridge? Thanks.

[Aric Dunn]

The NHC discussion has mentioned their southern bias the past few advisories, but I'll guess they will steer away from that very soon, and that will put the forecast track outside the area.

The forecasters base a lot on persistence, and Irma has been very persistent to the WNW and the reason the models are trending right, versus yesterday's more southern route...

Frank

I dont think they are going to change their thinking much. they know that tracks and set ups like this typically lead to longer more prononced westerly motion after the wsw to sw dive. There are a number of physical atributes that point to a southern route. Also dont forget that as this systems bottoms out of the sw dive it will be hitting peak intensity and likely will be pumping of that ridge to its north somewhat and models do not do well with that. It is still quite likely we see a shift south in models the next few runs expecially once it begins that turn to the WSW to SW.

Aric, could you please advise if I'm correct to assume that when you say "pumping of that ridge" that it means the storm could aid in intensifying or increasing the size of the ridge? Thanks.

the temporary strength of the ridge.

[Alyono]

Living in South Florida for most of my life, it's common knowledge that any storm at that far east and north usually (of course nothing is 100%, but usually) does not pose a threat, and why the local OCM (who is a meteorologist) made the comment.

P.S. Hope all is well in Poughkeepsie...

Frank

Frank, any reason why you don't think a storm passing through the Hebert Box is a threat when climo argues for 80% odds that it will impact the US? Just curious since the current location is a bit misleading to use climo with.

You are wrong about the hebert box. The rule is most storms to hit florida pass through the box. Not most storms to pass through the box strike the usa

[Alyono]

The NHC discussion has mentioned their southern bias the past few advisories, but I'll guess they will steer away from that very soon, and that will put the forecast track outside the area.

The forecasters base a lot on persistence, and Irma has been very persistent to the WNW and the reason the models are trending right, versus yesterday's more southern route...

Frank

Persistence was big 35 years ago when cliper was the best model

[txwatcher91]

Living in South Florida for most of my life, it's common knowledge that any storm at that far east and north usually (of course nothing is 100%, but usually) does not pose a threat, and why the local OCM (who is a meteorologist) made the comment.

P.S. Hope all is well in Poughkeepsie...

Frank

Frank, any reason why you don't think a storm passing through the Herbert Box is a threat when climo argues for 80% odds that it will impact the US? Just curious since the current location is a bit misleading to use climo with.

You are wrong about the hebert box. The rule is most storms to hit florida pass through the box. Not most storms to pass through the box strike the usa

Here are the stats from the article linked on here yesterday.

So what does all this mean when a hurricane passes or develops in the Hebert Box east of Puerto Rico since 1950?

1. N Carolina has as much of a chance to get hit as Florida.
2. 20.58% go out to sea without hitting land.
3. Only 8.82% make it into the Gulf of Mexico when they pass through the box as a hurricane.
4. Puerto Rico will get hit 20.58% of the time (the highest outside of N Antilles).

Here is the link. http://www.hurricanecity.com/hebertbox.htm

[JPmia]

Living in South Florida for most of my life, it's common knowledge that any storm at that far east and north usually (of course nothing is 100%, but usually) does not pose a threat, and why the local OCM (who is a meteorologist) made the comment.

I guess we'll know in a week or so, but until then the back and forth really isn't all that productive.

I happen to think it is productive as long as posters are backing their thoughts up with analysis. The mods here do a good job deleting the unproductive posts. This is a discussion forum.

[Ntxw]

Yeah the Herbert box mantras are a little misleading. Major Hurricanes that do hit Florida have high odds to have passed the box but not always, not that the storms that pass the box are likely to hit.

[Ntxw]

Irma will probably hold a fairly steady state with gradual strengthening (due to ideal atmospheric conditions). SSTs are modestly warm enough to sustain her. The real warm SSTs that maintains cat 4/5 for duration is W of 45W so once she passes that point she will likely take off assuming atmospheric conditions remains ideal.

[Blown Away]

I dont think they are going to change their thinking much. they know that tracks and set ups like this typically lead to longer more prononced westerly motion after the wsw to sw dive. There are a number of physical atributes that point to a southern route. Also dont forget that as this systems bottoms out of the sw dive it will be hitting peak intensity and likely will be pumping of that ridge to its north somewhat and models do not do well with that. It is still quite likely we see a shift south in models the next few runs expecially once it begins that turn to the WSW to SW.

Normally it takes a strong HP to push a system WSW in the mid Atlantic and don't the systems really accelerate ahead of that strong HP and normally don't see abrupt NW turns?

[txwatcher91]

Judging by the latest visible scans on Goes 16, it appears Irma is leveling off and moving west now, right on track for the NHC forecast point. The length of the WSW/SW turn will be key for the islands and future track as well.

[WeatherGuesser]

The real warm SSTs that maintains cat 4/5 for duration is W of 45W so once she passes that point she will likely take off assuming atmospheric conditions remains ideal.

I'd really like to see it hit 5 east of 54 so we can get that record, then die down and/or spin north to stay away from land.

[USTropics]

 https://twitter.com/TropicalTidbits/status/903614652042629120




Levi Cowan @TropicalTidbits
Clear eyewall replacement cycle occurring in #Irma this morning. Outer eyewall will compete with inner one for a while. Temporary weakening.
9:44 AM - Sep 1, 2017

[Ken711]

 https://twitter.com/BigJoeBastardi/status/903619704878751744

[SunnyThoughts]

 https://twitter.com/BigJoeBastardi/status/903619704878751744

Can't really bust with that cone.

[tolakram]

000
WTNT41 KNHC 011450
TCDAT1

Hurricane Irma Discussion Number 9
NWS National Hurricane Center Miami FL AL112017
1100 AM AST Fri Sep 01 2017

Irma is undergoing an eyewall replacement cycle. The small eye is
becoming less distinct, with both microwave and visible imagery
indicating the presence of a forming outer eyewall. Satellite
intensity estimates are lower, so the initial wind speed is reduced
to 95 kt. Some further weakening is possible over the next day or
so while Irma moves over marginally warm SSTs and continues the
eyewall replacement. After that time, the environment should be
generally conducive for some restrengthening, although forecasting
the timing of eyewall replacement cycles is next to impossible. The
biggest change from yesterday are the long-term wind shear
predictions from the global models, which shows a little more shear.
Still, the shear is not that strong, and the hurricane will be
moving over 29C SSTs. Thus, the NHC intensity forecast is reduced
somewhat from the previous one, but remains near or slightly above
the model consensus.

Irma has turned a little bit to the left, now estimated to be
moving 285/11. The general synoptic situation remains well
established due to a building mid-level high, which should cause
the hurricane to turn westward later today and then move
west-southwestward through the weekend. An upper-level low will be
dropping southward on the east side of that high, and should be a
key feature to how far south Irma goes before eventually turning
westward and west-northwestward early next week. There is a
noticeable clustering of guidance by day 5, with the ECMWF, HWRF and
corrected-consensus models to the south, and the UKMET, GFS, CTC and
HMON to the north. Since Irma is forecast to be a vertically deep
cyclone, it seems more likely to respond to the northerly flow from
the upper-level low, which leads me to believe the track will be on
the southern side of the guidance. Thus, the forecast will stay
similar to the previous one, very close to the southern cluster
mentioned above.


FORECAST POSITIONS AND MAX WINDS

INIT 01/1500Z 18.5N 37.8W 95 KT 110 MPH
12H 02/0000Z 18.7N 39.5W 90 KT 105 MPH
24H 02/1200Z 18.5N 41.8W 90 KT 105 MPH
36H 03/0000Z 18.0N 44.2W 95 KT 110 MPH
48H 03/1200Z 17.3N 46.6W 100 KT 115 MPH
72H 04/1200Z 16.2N 51.0W 105 KT 120 MPH
96H 05/1200Z 16.7N 55.2W 110 KT 125 MPH
120H 06/1200Z 18.0N 59.5W 110 KT 125 MPH

$$
Forecaster Blake

[SFLcane]

Blake sticking with a more southern route for IRMA

[Hurricane Andrew]

No longer forecasted to be a C4 within 5 days...interesting.

[wxman57]

Can see the double eyewalls here. I measured the inner eyewall at about 11 miles across. The outer eyewall is about 27 miles across.

Also, note that it's the Hebert box, not the HeRbert box. It's named after former NHC forecaster Paul Hebert. I met Paul at a National Hurricane Conference a number of years ago. Turns out we grew up only a few miles apart in south Louisiana.