ATL: IRMA - Post-Tropical - Discussion

[Hurricane Andrew]

As far as I know the USA has never been struck by two category 4 or higher hurricanes in the same year, however the USA has been struck by multiple major hurricanes in the same year. Not that any of this information means anything but it is still a interesting stat.

For years I was bringing up the equilibrium concept of hurricane seasons and after the 12 year "no majors hitting US" drought isn't it interesting that when one finally hit it wasn't just any category 3 TC, but what is guaranteed to be the costliest natural disaster in American history? Happens to be a rare (even more so) CAT4 strike. Whether or not Harvey was enough to make up for 12 years of no 100 knot winds occurring there is the question. Equilibrium - that's the policy.

Nature tends toward two things...equilibrium and chaos.

[Blinhart]

I know the NHC has Irma past 50W by Monday morning or so, I just don't see it going that fast I expect it to be closer to Tuesday morning or even evening before she gets to 50 W unless she doesn't take as much of a Northwestern trajectory and goes more of WNW or due W then might get to 50W by sometime Monday.

[Blinhart]

https://en.wikipedia.org/wiki/Hurricane ... _track.png

Just hope we don't see this

[chaser1]

Per records from 1851 through 2017, I found 51 TC's that moved between 14N and 20N when crossing 30W. Out of these 51, 6 (12%) hit the CONUS (5 of these 6 between 14N and 15N with the other being between 15N and 16N), 14 (27%) dissipated over open water, and 31 (61%) recurved east of the CONUS.

Interesting info. I'd also be curious about the number of higher latitude TC's having crossed 30W but eventually travelled WSW prior to striking the CONUS

[meriland29]

120hr

[Hurrilurker]

On satellite it looks like it's starting to miss forecast points to the south. It was supposed to start turning to the north but it doesn't look like that's happening yet, it appears to be continuing due west. It's IR though so hard to say, where the center is could be deceptive.

[beoumont]

On satellite it looks like it's starting to miss forecast points to the south. It was supposed to start turning to the north but it doesn't look like that's happening yet, it appears to be continuing due west. It's IR though so hard to say, where the center is could be deceptive.

Hmmmmm. Where's the center?

[ColdMiser123]

6z Best Track brings wind up to 60 KT and pressure down to 997 mb.

[mrbagyo]

This should be nearing Hurricane Status.
Irma is now sporting a microwave eye.

[KWT]

Very small core in there but the microwave imagery does show it is well formed! Could well be a hurricane now, the estimates may not be very high though given the small size of the convective coverage.

Could definatly do with a bit of beefing up on the convection front, but SST's aren't that high yet and there is that drier air still lurking to the NW.

Also worth noting the system is still at the same latitude, the advertised WNW/NW jump from the GFS simply hasn't happened. Looking to the north, the wind flow is still moving WSW though the main thrust of that now looks to the west of the system which may suggest it will gain some latitude later today. Worth watching though as it doesn't exactly build confidence if it is over-estimating WNW motion at just 6-12hr leads.

[jlauderdal]

nhc has been consistently on the southern side of guidance, they arent completely discounting the gfs but clearly are favoring the euro

[KWT]

nhc has been consistently on the southern side of guidance, they arent completely discounting the gfs but clearly are favoring the euro

I think that is quite wise at least in the short term, given the GFS has been trying to lift this NW for the last 24hrs and Irma hasn't shifted from near due west its clear that the GFS is seeing something that isn't as of yet happening.

[northjaxpro]

Yes, eye is in the process of emerging. Irma is such an extremely well organized cyclone! What a monster she is well on her way of becoming soon.

Irma I think is already a hurricane now or will be by the time the sun rises here on the U.S. East Coast this morning.

[USTropics]

5AM discussion is quite worrisome for the islands. NHC is going with a quick major and has currently sided with the more southern side of the guidance suite.

ZCZC MIATCDAT1 ALL
TTAA00 KNHC DDHHMM

Tropical Storm Irma Discussion Number 4
NWS National Hurricane Center Miami FL AL112017
500 AM AST Thu Aug 31 2017

Irma continues to become better organized with a developing CDO and
a few banding features. The overall cloud pattern is fairly
symmetric, with fair upper-level outflow over all but the
southeastern portion of the circulation. The current intensity
is set at 60 kt, which is the mean of Dvorak estimates from TAFB
and SAB. The environment ahead of Irma appears to be mostly
conducive for intensification, with increasingly warm SSTs.
Vertical shear is expected to remain low as an upper-level trough
to the west-northwest of the tropical cyclone lifts out to the
north and west. The only noticeable inhibiting factor is slightly
drier mid-level air in 2-5 days, but this will probably not be much
of a deterrent for strengthening. The official intensity forecast
follows the latest consensus of the models, and is similar to the
previous NHC prediction.

Based on geostationary satellite fixes, the initial motion is just
slightly north of west or 280/10 kt. Most of the track guidance
shows a west-northwestward motion for the next day or so. Irma
will remain situated to the south of a well-defined
mid-tropospheric ridge through the forecast period. Much of the
guidance indicates that Irma will turn toward a slightly south of
westward heading in a couple of days, presumably in response to some
building of high pressure to the north and northwest. The official
track forecast also shows this, and remains on the southern side of
the guidance suite. This is mainly a blend of the GFS and ECMWF
solutions.

FORECAST POSITIONS AND MAX WINDS

INIT 31/0900Z 16.5N 32.9W 60 KT 70 MPH
12H 31/1800Z 17.0N 34.2W 70 KT 80 MPH
24H 01/0600Z 17.6N 36.0W 80 KT 90 MPH
36H 01/1800Z 18.0N 37.9W 85 KT 100 MPH
48H 02/0600Z 18.2N 40.1W 90 KT 105 MPH
72H 03/0600Z 17.5N 45.0W 100 KT 115 MPH
96H 04/0600Z 16.7N 49.5W 105 KT 120 MPH
120H 05/0600Z 16.0N 53.5W 105 KT 120 MPH

$$
Forecaster Pasch

[KWT]

Looks like to me 280 is about right, its certainly not gaining any major latitude yet still and the flow to the north isn't really suggestive of that changing just yet to any major degree.

Also NHC are dropping this quite low, down to 16N, its from that point onwards uncertainty really creeps up regarding how much of a lift up it takes, though if it really is down at 16N at that point I'm struggling to see it turning as much as the GFS wants it to.

Togive an idea of where the GFS is in relation to the NHC, the NHC is at 16N at 54W, the GFS is up over 18N at the same time....

[jlauderdal]

nhc has been consistently on the southern side of guidance, they arent completely discounting the gfs but clearly are favoring the euro

I think that is quite wise at least in the short term, given the GFS has been trying to lift this NW for the last 24hrs and Irma hasn't shifted from near due west its clear that the GFS is seeing something that isn't as of yet happening.

yes, will be interesting to see the initialization on the next gfs output..

[GCANE]

Looks like Irma will latch into some ventilation from the ULL developing to its NE.
That ULL is forecast to strengthen and develop a poleward outflow channel.
The other ULL, to Irma's NW, will move in tandem with Irma and is forecast to dissipate near the Bahamas.
Looks like it'll open up a door for strong strengthening of Irrma as it approaches the coast.
Run-to-run has been very consistent with upper air forecast.
Hopefully, the now-forecasted low in the Carolinas will sweep Irma out to sea.

[KWT]

Worth noting the ECM doesn't even form that low you mention GCANE...

As you say there is a nice set-up aloft for strengthening and its no wonder the GFS and most other models have been developing this quite strongly in recent runs as the set-up does suggest a major hurricane is upcoming.

[USTropics]

First visible image of the morning, definite signs of an eye trying to form:

[GCANE]

Worth noting the ECM doesn't even form that low you mention GCANE...

As you say there is a nice set-up aloft for strengthening and its no wonder the GFS and most other models have been developing this quite strongly in recent runs as the set-up does suggest a major hurricane is upcoming.

I know its far out yet, but GFS has it going negative tilt and then cutoff.
Going to watch run-to-run if consistent.
If Irma stays a bit weaker, which I think it will due to mid-level dry air along its track, Irma could avoid this.