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Major Hurricane Irma

NJwx85

By NJwx85,
in Tropical Headquarters

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Hoosier

Hoosier

Posted
Posted
12 minutes ago, donsutherland1 said:

As of this afternoon, my thinking is that East Coast landfall remains more likely than not (approximately a 60% probability). The Southeast (especially in an area running from Georgia to North Carolina) is probably much more likely to see landfall than an area running from Virginia to New England.

However, I don't think the 12z ECMWF can be dismissed outright. Whether a deep low forms over eastern Canada could hold the key. Looking back to past storms, there's one potential close fit to what the ECMWF is showing: Hurricane #6 in 1866, which peaked as a Category 4 storm before recurving sharply away from the U.S. East Coast.

Irma-ECMWF0903201712z.jpg

Excellent find, Don.  And only had to go back 150 years to find it.  :P  Thanks for posting.

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yoda

yoda

Posted
Posted 
HURRICANE IRMA FORECAST/ADVISORY NUMBER  18
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL112017
2100 UTC SUN SEP 03 2017

CHANGES IN WATCHES AND WARNINGS WITH THIS ADVISORY...

THE GOVERNMENT OF ANTIGUA HAS ISSUED A HURRICANE WATCH FOR THE
ISLANDS OF ANTIGUA... BARBUDA... ANGUILLA... MONTSERRAT... ST.
KITTS... AND NEVIS.

THE GOVERNMENT OF THE NETHERLANDS HAS ISSUED A HURRICANE WATCH FOR
THE ISLANDS OF SABA... ST. EUSTATIUS... AND SINT MAARTEN.

THE GOVERNMENT OF FRANCE HAS ISSUED A HURRICANE WATCH FOR ST.
MARTIN AND SAINT BARTHELEMY.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A HURRICANE WATCH IS IN EFFECT FOR...
* ANTIGUA... BARBUDA... ANGUILLA... MONTSERRAT... ST. KITTS... AND
NEVIS
* SABA... ST. EUSTATIUS... AND SINT MAARTEN
* SAINT MARTIN AND SAINT BARTHELEMY
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RUNNAWAYICEBERG

RUNNAWAYICEBERG

Posted
Posted
1 minute ago, UpstateSCBud said:

Very happy to see the Euro taking this OTS. I'm headed to the Isle of Palms near Charleston in 6 days and I don't need a hurricane messing up my vacation.

Probably best not to hang your hat on an op run at this lead time. And the euro fwiw has been all over the place with this. 

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yoda

yoda

Posted
Posted 
Hurricane Irma Discussion Number  18
NWS National Hurricane Center Miami FL       AL112017
500 PM AST Sun Sep 03 2017

The satellite presentation of Irma has degraded slightly since
this morning with the eye becoming less defined.  There is evidence
of some northerly flow beneath the cirrus outflow, which may be
disrupting the inner core and preventing Irma from strengthening.
The latest consensus of the Dvorak satellite estimates suggest that
the 100 kt initial intensity could be a little generous, but with a
NOAA aircraft headed into the hurricane it is best to wait until
data from that mission is received before making any adjustment to
the initial wind speed.

Irma has been moving more westward since the previous advisory, but
the longer-term motion estimate is still south of due west or
260/12 kt.  A strong high pressure ridge over the central Atlantic
should steer Irma westward to west-southwestward during the next
couple of days.  After that time, a turn toward the west-northwest
should occur as Irma approaches the western portion of the Atlantic
ridge.  The cross-track spread of the guidance is still relatively
small through day 5, but the ECMWF, UKMET, and HWRF are on the
southern side of the guidance envelope, with the GFS near the
middle of the envelope.  The latest NHC track is once again near
the consensus of these typically reliable models, which is between
the southern edge of the guidance and the TCVN multi-model
consensus.  The updated track is not very different from the
previous advisory, except at day 5 where it is slightly west of
the previous forecast.

Users are reminded to not focus on the exact forecast track since
strong winds and heavy rainfall extend well away from the center.
In fact, ASCAT data that arrived after the issuance of the previous
advisory indicated that the size of the tropical-storm-force wind
field has expanded, especially over the northern semicircle.  As a
result, the initial and forecast wind radii have been adjusted
accordingly.


KEY MESSAGES:
1. Irma is expected to impact the northeastern Leeward Islands by
the middle of this week as a major hurricane, accompanied by
dangerous wind, storm surge, and rainfall impacts, along with rough
surf and rip currents.  Hurricane watches have been issued for
portions of the Leeward Islands and additional hurricane or tropical
storm watches may be required on Monday.  Residents in these areas
should monitor the progress of Irma and listen to advice given by
officials.

2. Irma is expected to remain a dangerous major hurricane through
the upcoming week and could directly affect the British and U.S.
Virgin Islands, Puerto Rico, Hispaniola, the Turks and Caicos, and
the Bahamas. Residents in all of these areas should monitor the
progress of Irma and listen to advice given by officials.  Tropical
storm or hurricane watches could be issued for the British and U.S.
Virgin Islands and Puerto Rico on Monday.

3. It is too early to determine what direct impacts Irma might have
on 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  03/2100Z 17.6N  49.8W  100 KT 115 MPH
 12H  04/0600Z 17.2N  51.4W  105 KT 120 MPH
 24H  04/1800Z 16.8N  53.5W  110 KT 125 MPH
 36H  05/0600Z 16.8N  55.8W  115 KT 130 MPH
 48H  05/1800Z 17.3N  58.2W  120 KT 140 MPH
 72H  06/1800Z 19.1N  63.5W  120 KT 140 MPH
 96H  07/1800Z 21.2N  68.8W  115 KT 130 MPH
120H  08/1800Z 23.0N  73.5W  115 KT 130 MPH

$$
Forecaster Brown
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bdgwx

bdgwx

Posted
Posted
7 minutes ago, RUNNAWAYICEBERG said:

Probably best not to hang your hat on an op run at this lead time. And the euro fwiw has been all over the place with this. 

I don't know...the Euro is annihilating the IVCx consensus and official NHC forecasts in D3-D5 skill according to verification stats for Irma.

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SN_Lover

SN_Lover

Posted
Posted
7 minutes ago, yoda said: 

Hurricane Irma Discussion Number  18
NWS National Hurricane Center Miami FL       AL112017
500 PM AST Sun Sep 03 2017

The satellite presentation of Irma has degraded slightly since
this morning with the eye becoming less defined.  There is evidence
of some northerly flow beneath the cirrus outflow, which may be
disrupting the inner core and preventing Irma from strengthening.
The latest consensus of the Dvorak satellite estimates suggest that
the 100 kt initial intensity could be a little generous, but with a
NOAA aircraft headed into the hurricane it is best to wait until
data from that mission is received before making any adjustment to
the initial wind speed.

Irma has been moving more westward since the previous advisory, but
the longer-term motion estimate is still south of due west or
260/12 kt.  A strong high pressure ridge over the central Atlantic
should steer Irma westward to west-southwestward during the next
couple of days.  After that time, a turn toward the west-northwest
should occur as Irma approaches the western portion of the Atlantic
ridge.  The cross-track spread of the guidance is still relatively
small through day 5, but the ECMWF, UKMET, and HWRF are on the
southern side of the guidance envelope, with the GFS near the
middle of the envelope.  The latest NHC track is once again near
the consensus of these typically reliable models, which is between
the southern edge of the guidance and the TCVN multi-model
consensus.  The updated track is not very different from the
previous advisory, except at day 5 where it is slightly west of
the previous forecast.

Users are reminded to not focus on the exact forecast track since
strong winds and heavy rainfall extend well away from the center.
In fact, ASCAT data that arrived after the issuance of the previous
advisory indicated that the size of the tropical-storm-force wind
field has expanded, especially over the northern semicircle.  As a
result, the initial and forecast wind radii have been adjusted
accordingly.


KEY MESSAGES:
1. Irma is expected to impact the northeastern Leeward Islands by
the middle of this week as a major hurricane, accompanied by
dangerous wind, storm surge, and rainfall impacts, along with rough
surf and rip currents.  Hurricane watches have been issued for
portions of the Leeward Islands and additional hurricane or tropical
storm watches may be required on Monday.  Residents in these areas
should monitor the progress of Irma and listen to advice given by
officials.

2. Irma is expected to remain a dangerous major hurricane through
the upcoming week and could directly affect the British and U.S.
Virgin Islands, Puerto Rico, Hispaniola, the Turks and Caicos, and
the Bahamas. Residents in all of these areas should monitor the
progress of Irma and listen to advice given by officials.  Tropical
storm or hurricane watches could be issued for the British and U.S.
Virgin Islands and Puerto Rico on Monday.

3. It is too early to determine what direct impacts Irma might have
on 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  03/2100Z 17.6N  49.8W  100 KT 115 MPH
 12H  04/0600Z 17.2N  51.4W  105 KT 120 MPH
 24H  04/1800Z 16.8N  53.5W  110 KT 125 MPH
 36H  05/0600Z 16.8N  55.8W  115 KT 130 MPH
 48H  05/1800Z 17.3N  58.2W  120 KT 140 MPH
 72H  06/1800Z 19.1N  63.5W  120 KT 140 MPH
 96H  07/1800Z 21.2N  68.8W  115 KT 130 MPH
120H  08/1800Z 23.0N  73.5W  115 KT 130 MPH

$$
Forecaster Brown

Looks like the it's the same feature kept Harvey in check in the Caribbean, and when it went away, we all know what happened.

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jojo762

jojo762

Posted
Posted

Curious to see where NHC starts taking the OFCL and the cone in the next 24 hours as the D5 forecast will start to impinge on when Irma has been modeled to start turning right some (unless you believe the GEFS/EPS members that take it into FL). 

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donsutherland1

donsutherland1

Posted
Posted
5 minutes ago, WxWatcher007 said:

Nice post. I'm a little lower on the odds of a US landfall (40%) based on climo and the uncertainty that exists with the handling of upper level features at this range. Many have tried, but few storms have succeeded in getting all the way across the Atlantic as you know. I did a longer post in my regional thread, but I'd like to see the 3 things happen before starting to feel more confident in the guidance and UL pattern evolution:

1) I need to see where and when Irma begins its semi-permanent WNW heading. That'll allow us to model and extrapolate with more accuracy. 

2) I need to see how close Irma gets to my benchmark of the Central Bahamas. The further south this is, the harder it becomes for an OTS track IMO.

3) I need to see what happens with the PAC-CONUS pattern once the players are on the field. We're going to have a better sense in a few days. 

Threat no doubt at this range, but we'll see if that holds. 

I agree with much of what you wrote. Of course, whether one is estimating a 40% or 60% probability of landfall, that's far above climatology for a tropical cyclone in the vicinity of Irma's current position. My 60% is sort of a compromise between the individual EPS and GEFS members, operational ECWMF and GFS, and climatology. The Pacific-CONUS pattern you cited will be crucial in determining the track Irma takes. I suspect that we'll begin to have greater model consensus and consistency developing around Wednesday or Thursday. A lot can still happen.

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