ATL: IRMA - Post-Tropical - Discussion

[cycloneye]

BULLETIN
Hurricane Irma Advisory Number 13
NWS National Hurricane Center Miami FL AL112017
1100 AM AST Sat Sep 02 2017

...IRMA MOVING WESTWARD ACROSS THE ATLANTIC AS A SMALL HURRICANE...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...18.8N 43.3W
ABOUT 1220 MI...1965 KM E OF THE LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...110 MPH...175 KM/H
PRESENT MOVEMENT...W OR 265 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...973 MB...28.74 INCHES
----------------------------------------------------------


Hurricane Irma Discussion Number 13
NWS National Hurricane Center Miami FL AL112017
1100 AM AST Sat Sep 02 2017

Hurricane Irma continues to display an eye within a small central
dense overcast in the visible and infrared imagery from the GOES
and METEOSAT satellites. Dvorak current intensity numbers from
TAFB, SAB, and the CIMSS ADT have not changed, so the intensity
remains 95 kt.

The environment in which Irma is embedded shows mixed signals for
the next few days. While the vertical shear remains low through
Monday, the SSTs are lukewarm and mid-level humidities are dry.
(Indeed an overnight SSMIS microwave pass showed a distinct finger
of dry air wrapping around the south side of Irma not far from its
inner core.) However, after the waters warm and the atmosphere
moistens at days 3-5, the shear is forecast to go up. The guidance
has substantial spread between Category 2 and 4 by the end of the
forecast period. The official intensity forecast is based upon a
blend of the LGEM/DSHP statistical techniques and the HWRF dynamical
model and is unchanged from the previous advisory.

Irma is finally moving slightly south of due west at 13 kt. A
large, building Azores-Bermuda high should turn Irma toward the
west-southwest at a slower rate of speed during the next two days.
By days 3 to 5, Irma should be rounding the southwestern periphery
of the high and start turning back toward the west-northwest. The
track guidance is in tight agreement with this scenario and the
official forecast is a simply an update from the previous advisory.

Irma is a small hurricane, as observed by ship BATFR17 and the
overnight ASCAT scatterometer pass with tropical-storm-force winds
extending out at most about 60 nm. The official size forecast is
based upon the RVCN multi-model consensus technique.

KEY MESSAGES:

1. Irma is expected to be a major hurricane when it moves closer to
the Lesser Antilles early next week, producing rough surf and rip
currents. Irma could also cause dangerous wind, storm surge, and
rainfall impacts on some islands, although it is too soon to specify
where and when those hazards could occur. Residents in the Lesser
Antilles should monitor the progress of Irma through the weekend and
listen to any advice given by local officials.

2. It is much too early to determine what direct impacts Irma will
have on the Bahamas and the continental United States. Regardless,
everyone in hurricane-prone areas should ensure that they have their
hurricane plan in place, as we are now near the peak of the season.


FORECAST POSITIONS AND MAX WINDS

INIT 02/1500Z 18.8N 43.3W 95 KT 110 MPH
12H 03/0000Z 18.5N 45.0W 95 KT 110 MPH
24H 03/1200Z 18.0N 47.4W 100 KT 115 MPH
36H 04/0000Z 17.4N 49.5W 105 KT 120 MPH
48H 04/1200Z 17.1N 51.6W 110 KT 125 MPH
72H 05/1200Z 17.4N 56.0W 110 KT 125 MPH
96H 06/1200Z 19.2N 60.6W 115 KT 130 MPH
120H 07/1200Z 22.0N 66.0W 115 KT 130 MPH

$$
Forecaster Landsea

[Hurricane Andrew]

Interesting...looks like this may not get as strong as initially thought. To me, it really looks like its struggling.

[Jimsot]

02/1145 UTC 18.8N 42.5W T5.0/5.0 IRMA -- Atlantic

Looks like more west than NHC 5 am Position... and little South.

Hi Gusty, Msbee, and Cyclone Eye. I haven't been around since we moved back to the US from Anguilla after 10 wonderful years there. Very worried for all my friends in the Caribbean a close call at the very least. Of course some models say Irma might visit us here in SC. Everyone stay prepared and safe.

[RL3AO]

Interesting...looks like this may not get as strong as initially thought. To me, it really looks like its struggling.

It's behaving exactly as expected. The water is barely warm enough to support a major hurricane right now.

[cycloneye]

[Hurricane Andrew]

Interesting...looks like this may not get as strong as initially thought. To me, it really looks like its struggling.

It's behaving exactly as expected. The water is barely warm enough to support a major hurricane right now.

SHIPS has 20kt of shear in 72hrs...I wonder if that would even touch a storm like this.

[wxman57]

I think that Luis is going to be OK there in PR. Irma is still a relatively small storm. It's likely to pass 100-150nm north of San Juan. Far enough that TS winds will pass to the north. Could pass close enough to produce 40-50 mph sustained wind there, though.

As for the East U.S. Coast, the big question is timing. Timing of the trof/front along the east coast and Irma's arrival. A faster Irma and/or slower front/trof would mean recurve. If Irma is slower and/or the trof/front is faster, then high pressure builds north of Irma late next week, blocking recurve and shoving Irma west. I'm thinking that a US landfall is more likely than not, maybe 54% east coast landfall, 44% recurve, 2% into Gulf. I don't think that the timing is right for a Florida hit, as Irma may be north of 30N before it could be blocked. That puts SC northward under the gun.

Heading out on my bike shortly to survey the Brays Bayou flooding area. This is my first day off since weekend before last. Twelve days of 12+ hr shifts. Flooding is still bad here. Only 33" at my house. Wow! Only? Street flooding was all I saw here. However, 1/4 to 1/2 mile around me north or south and houses flooded. They're saying some homes may remain flooded for weeks on the west side.

thanks for our post wxman57. would you also feel that we will be ok here in St Maarten?
I cannot imagine how exhausted you must be. what a tragedy in Texas. Everyone's thoughts are with all of you

I think so, msbee. Very good agreement and consistency in the WNW track passing to your north. Obviously, pay close attention in case something unforeseen happens.

[hohnywx]

Interesting...looks like this may not get as strong as initially thought. To me, it really looks like its struggling.

It's behaving exactly as expected. The water is barely warm enough to support a major hurricane right now.

SHIPS has 20kt of shear in 72hrs...I wonder if that would even touch a storm like this.

I would think not...for a storm as strong as Irma, it should not have a deleterious effect.

[tropicwatch]

I am kind of surprised they with a west movement and not wsw. Satellite appears pretty clearly more of a wsw movement unless I am missing something.

[WeatherLovingDoc]

Where do they fly out of and return to? Miami? thanks.

[cycloneye]

Where do they fly out of and return to? Miami? thanks.

They will takeoff and return to Barbados and the same in St Croix.

[mpic]

Thank you so much for the advice, this couldn't have been more helpful!

Another tip (just went through Harvey) I cleaned out all.my big outside trash cans to catch water to use for flushing the toilet. I have a well so couldn't flush when the electricity went out.

[clipper35]

We have to take in consideration that most of the data nhc is receiving is coming from ships,satellite. Once they receive recon data input we will know how strong she is and future intensification probabilities.

[mrbagyo]

Definitely a very small storm. This is a technical meteorological question/observation: what would occur to cause Irma to grow in size? The models seem to depict a very large system east of the US in several days. It surprises me since right now it is persistently so small and despite the many prognostications on this board about it growing after ERC, it hadn't/isn't happening. So I'm curious what factors come into play to cause s storm to grow in size? I know intensity has nothing to do with overall size- see Camille, Andrew, Charley as examples or potent small storms.

Put in lots of moisture and it would likely expand.
Right now dry air is trying to envelop around the system thus limiting convection- SST isnt optimal either.
The entire circulation doesn't look really small (But CDO / core is) to me at least in visible image - low level inflow just struggling to produce enough convection with the limited moisture.
It's kinda difficult to expand if the convection isn't sufficient

[psyclone]

I'm definitely feeling better based on the Euro ensembles and other models for areas south of the Savannah river. Things are trending in our favor (recognizing that there is ample time for things to trend back the other way)...this could end up as another storm that grazes or rakes portions of the Bahamas and leaves Florida unscathed. I suspect Florida will get a good scare (and perhaps more) this year but it will be later this season...and not from the east but from the south..

[NDG]

By no means I will be stupid enough to say that FL is in the clear by going by the models' past 5 days forecast, a lot can still change like a weaker trough and stronger ridging to the north of Irma in the 7-10 day range which not even the Euro is King in that range.
A great example was Harvey, the GFS and Euro started pointing towards TX only within their 5-6 day range.

[AxaltaRacing24]

By no means I will be stupid enough to say that FL is in the clear by going by the models' past 5 days forecast, a lot can still change like a weaker trough and stronger ridging to the north of Irma in the 7-10 day range which not even the Euro is King in that range.
A great example was Harvey, the GFS and Euro started pointing towards TX only within their 5-6 day range.

I will never make that mistake ever again after the Matthew scare last year.

[NDG]

By no means I will be stupid enough to say that FL is in the clear by going by the models' past 5 days forecast, a lot can still change like a weaker trough and stronger ridging to the north of Irma in the 7-10 day range which not even the Euro is King in that range.
A great example was Harvey, the GFS and Euro started pointing towards TX only within their 5-6 day range.

I will never make that mistake ever again after the Matthew scare last year.

I wouldn't call Matthew just a scare, still ended doing a lot of damage to immediate coastal communities in central and NE FL.

[Kazmit]

Definitely moving WSW now.

[otowntiger]

I'm definitely feeling better based on the Euro ensembles and other models for areas south of the Savannah river. Things are trending in our favor (recognizing that there is ample time for things to trend back the other way)...this could end up as another storm that grazes or rakes portions of the Bahamas and leaves Florida unscathed. I suspect Florida will get a good scare (and perhaps more) this year but it will be later this season...and not from the east but from the south..

or, more likely southwest ala Charley.