Major Hurricane Irma

[BuffaloWeather]

Just now, heavy_wx said:

Those were all in the Gulf/Caribbean. The poster specifically asked for sub-900 mb storms in the Atlantic Ocean.

The rarity of sub-900 mb storms in the North Atlantic is an indication that these aggressive model forecasts are unlikely to occur, never mind that some of these forecasts stretch the bounds of what's physically possible in this part of the world.

Andrew would be a good example of what Irma might do, albeit Andrew might be a bit south of where Irma possibly hits. Andrew had 926 MB with wind speeds of 165 mph. While Harvey hit at 130 MPH with 938 MB. All depends on a number of factors with wind speeds in Hurricanes. 

[LibertyBell]

7 minutes ago, BuffaloWeather said:

Andrew would be a good example of what Irma might do, albeit Andrew might be a bit south of where Irma possibly hits. Andrew had 926 MB with wind speeds of 165 mph. While Harvey hit at 130 MPH with 938 MB. All depends on a number of factors with wind speeds in Hurricanes. 

Small size of Andrew enabled those amazing wind speeds.  Small size means a much greater slope of pressure change between the storm and its environment, therefore stronger winds- it was similar to a large tornado.

 

[Hazey]

Those were all in the Gulf/Caribbean. The poster specifically asked for sub-900 mb storms in the Atlantic Ocean.

The rarity of sub-900 mb storms in the North Atlantic is an indication that these aggressive model forecasts are unlikely to occur, never mind that some of these forecasts stretch the bounds of what's physically possible in this part of the world.

Everything is thought be impossible until it happens for the first time. There has to be something to these sub 900 model depictions. It's not just one model having a blip run. It's the consistency that is hard to ignore.

[packfan98]

12 minutes ago, Wow said:

18z GEFS made quite an improvement on coming in general agreement, narrowing it down to the SE. No OTS tracks.  Not to say it won't make additional moves (and it will).  A bit alarming to see so many members bring a sub-965mb hurricane into CAE, CLT, and RDU. Even got a couple into ATL!

The biggest net result difference in the GFS and EURO suites is that the GFS members all have NW movement after landfall and the Euro members have a more natural looking NE movement.

[JasonOH]

Just now, LibertyBell said:

Small size of Andrew enabled those amazing wind speeds.  Small size means a much greater slope of pressure change between the storm and its environment, therefore stronger winds- it was similar to a large tornado.

 

Pretty much. When there's a smaller storm, the distance between isobars is smaller, so the Pressure Gradient Force is greater than a larger storm with the same minimum and environmental pressures.

[Rtd208]

DT (WxRisk) Sunday Irma Update

https://www.wxrisk.com/sunday-sept-3-update-on-irma-and-the-risk-to-se-usa/

[LibertyBell]

1 hour ago, LakeEffectKing said:

 

Nice stat.  I think Irma will have some special characteristics wrt pressure/wind relationship.  (If current modeling of "long duration" low pressures through the Bahamas occur)

All models show Irma gaining significant size, thus creating a larger, lower pressure environment, wrt the core....thus with pressures substantially lower than that a normal hurricane (say 100-200 miles from the center) the pressure change over distance from there to the core may not be quite as tight as you'd get with a cane in a higher pressure environment, or a cane that has explosively developed (ie Wilma), thus the wind speeds may be a tad lower than the traditional/normal pressure/wind relationship.

 

Edit:  And I'm talking about Irma when she is north of the Bahamas.....as she approaches them and enters them, I think CAT 5 winds are certainly possible (again, assuming the model outputs of low 900's verify)

Patricia in the Pac also had special characteristics with pressure/wind but it was in the opposite direction lol.

[Wow]

6 minutes ago, packfan98 said:

The biggest net result difference in the GFS and EURO suites is that the GFS members all have NW movement after landfall and the Euro members have a more natural looking NE movement.

GFS lets the deep south ULL and ridge building overhead to win out as the main trough pulls quickly away.  Euro keeps the main trough in play by digging it farther south over SE Canada, and so keeps the OTS lane open.

[TriPol]

1 hour ago, NJwx85 said:

My God, HWRF is at 864mb hr 120...

Not that it would ever happen, but that's Typhoon Tip territory.

[winterymix]

7 minutes ago, Wow said:

GFS lets the deep south ULL and ridge building overhead to win out as the main trough pulls quickly away.  Euro keeps the main trough in play by digging it farther south over SE Canada, and so keeps the OTS lane open.

If the GFS has the right idea, northern NC and S VA could get an inch an hour for a minimum of six hours.

[LibertyBell]

2 hours ago, Windspeed said:

Yes. Barometers were pretty common place by the 1860s in ports, island communties and especially ships. Though far from perfect, logs were reconstructed to get an idea of location, track and intensity. Obviously things got a lot better communication-wise with telegraph lines and an organized bureau. Still, many intense storms were likley never recorded away from land or in the absence of ships.


Back to Irma, the most important info out of the VDM was the pressure and size of the eyewall. 958 with a 30nm diameter without a concentric feature. If cloud debris can clear out this may deepen significantly.

This is a fascinating discussion, and Pazzo brought up a good point about when have we ever seen a sub900mb in the Atlantic Ocean (not basin.)  The only one that comes to mind to me is the 1935 Labor Day Hurricane which was technically in the Florida Straits, so not sure if that counts.  Back in the 1840s we had an extremely powerful Cat 5 hurricane hit Cuba called The Great Havana Hurricane, that might be a contender too, though we have no idea what its exact pressure at maximum intensity was of course.  Below they list lowest pressure at 938mb but that obviously wouldn't be the lowest pressure if it's a Cat 5.

https://en.wikipedia.org/wiki/1846_Havana_hurricane

The 1846 Havana hurricane (also known as the Great Havana hurricane of 1846, San Francisco de Borja hurricane and The Great Gale of 1846) was the most intense tropical cyclone in recorded history for 78 years and the first known Category 5-strength hurricane to strike Cuba. The first indications of the formation of a disturbance were first noted on 5 October in the Caribbean Sea, but little else was known until the storm approached Cuba on 10 October. There, it brought extreme winds and the lowest knownatmospheric pressure of the time – 938 mbar (27.70 inHg) – a record which remained unbroken until the development of a later cyclone in 1924. It soon curved toward Florida, where it maintained its intensity, continuing to rapidly hasten northward along theEast Coast of the United States to New England. It entered an extratropical transition while situated over New York on 13 October, producing intense Category 2-force winds and unusually little precipitation. Eventually, the gale dissipated over the Canadian Maritimes the following day as a markedly weaker storm.

 

https://en.wikipedia.org/wiki/1924_Cuba_hurricane

Here's another one, though this was obviously a Caribbean storm, lowest pressure was 910mb.

 

[heavy_wx]

10 minutes ago, Hazey said:

Everything is thought be impossible until it happens for the first time. There has to be something to these sub 900 model depictions. It's not just one model having a blip run. It's the consistency that is hard to ignore.

It looks like the 12z and 00z Euro runs have been in the 920 mb range; I only have access to 24-hour forecast increments, but it doesn't appear that the Euro has been nearly as intense with Irma as the GFS and its high-resolution derivatives. Perhaps it's possible that Irma reaches a MSLP < 900 mb, but given the Euro model guidance and climatology, I think it's very unlikely.

[audioguy3107]

Good write up by DT except I don't see the WSW movement ending one bit.  If you loop the satellite it's still clearly moving WSW.

[kvegas-wx]

Nice dose of reality from DT.  Everyone here hoping for a LF (God only knows why) should read it and understand the biases of the GFS and the historical preference granted to the Euro for correctly sniffing out some unusual storms.  OTS is ABSOLUTELY still on the board here!

[Wow]

4 minutes ago, audioguy3107 said:

Good write up by DT except I don't see the WSW movement ending one bit.  If you loop the satellite it's still clearly moving WSW.

Correct - she's still got some southward movement.  Official track continues her southward movement until late Monday/early Tuesday

[Westendsnowguy]

6 minutes ago, audioguy3107 said:

Good write up by DT except I don't see the WSW movement ending one bit.  If you loop the satellite it's still clearly moving WSW.

Didnt think it was that good......he also stated last nights euro was the third in a row to not make US landfall

[Morris]

Recon clearly showed the WSW movement with the 3 eye fixes.

[LandofLincoln]

7 minutes ago, kvegas-wx said:

Nice dose of reality from DT.  Everyone here hoping for a LF (God only knows why) should read it and understand the biases of the GFS and the historical preference granted to the Euro for correctly sniffing out some unusual storms.  OTS is ABSOLUTELY still on the board here!

Hard to really give the Euro too much credit right now considering it's been kind of all over the place, so you can't say it's really been predicting anything.

[HillsdaleMIWeather]

2 minutes ago, LandofLincoln said:

Hard to really give the Euro too much credit right now considering it's been kind of all over the place, so you can't say it's really been predicting anything.

A thing to remember is all the models have their respective biases too

[RU848789]

59 minutes ago, BuffaloWeather said:

GFS/EURO/GEM ENS all have it going into Bahamas riding up Florida and hitting the SE Coast around Georgia/SC. Pretty solid consensus right there. 

Except that the Euro parallels the FL/GA/SC/NC coasts (kind of like Matthew last year) before heading ENE well off the Outer Banks at 240 hours, the end of its run - but there's no way the storm is coming back west with that track and forward speed to the ENE.  So, nowhere near consensus, especially if the Euro is not on board. 

 

[bdgwx]

7 minutes ago, LandofLincoln said:

Hard to really give the Euro too much credit right now considering it's been kind of all over the place, so you can't say it's really been predicting anything.

Forecast verification stats for Irma show that the Euro has been outperforming all other models, the TVCx consensus, and even the official NHC forecasts for most of lead times right now.

[TellicoWx]

Didn't really understand the part about current motion affecting model correction later down the road. As many respected posters here have stated, the track correcting east or west is due to how the H5 plays out with the trough and ull, not current motion.

[RU848789]

8 minutes ago, bdgwx said:

Forecast verification stats for Irma show that the Euro has been outperforming all other models, the TVCx consensus, and even the official NHC forecasts for most of lead times right now.

Just curious if there is some source for this statement - pages are going by so fast, I might have missed it earlier - thanks...

[LakeEffectKing]

12 minutes ago, RU848789 said:

Except that the Euro parallels the FL/GA/SC/NC coasts (kind of like Matthew last year) before heading ENE well off the Outer Banks at 240 hours, the end of its run - but there's no way the storm is coming back west with that track and forward speed to the ENE.  So, nowhere near consensus, especially if the Euro is not on board. 

 

He was talking about the global ensemble means....there is good consensus with them ATT.  The operational runs, for all models have wavered quite a bit, which is to be expected at these leads.

[Wow]

Trend of the GEFS members comparing 18z to 0z...

[bdgwx]

6 minutes ago, RU848789 said:

Just curious if there is some source for this statement - pages are going by so fast, I might have missed it earlier - thanks...

From: http://www.atmos.albany.edu/facstaff/tang/tcguidance/

UKMET has been doing well too, but the NHC is beating it at 96 hours. We should have the 120 hour verifications tomorrow evening. You can also see that NHC has positive skill compared to the TVCN consensus at least at 72 and 96 hours. That doesn't always happen.

[RU848789]

5 minutes ago, LakeEffectKing said:

He was talking about the global ensemble means....there is good consensus with them ATT.  The operational runs, for all models have wavered quite a bit, which is to be expected at these leads.

Yep, didn't notice the "ENS" part of his post. 

[40/70 Benchmark]

34 minutes ago, heavy_wx said:

It looks like the 12z and 00z Euro runs have been in the 920 mb range; I only have access to 24-hour forecast increments, but it doesn't appear that the Euro has been nearly as intense with Irma as the GFS and its high-resolution derivatives. Perhaps it's possible that Irma reaches a MSLP < 900 mb, but given the Euro model guidance and climatology, I think it's very unlikely.

My guess is this peaks at 920/150....high-end cat 4

[donsutherland1]

For purposes of climatology, 39 hurricanes passed within 100 nautical miles of Irma’s 8 pm position (17.4°N 50.3°W). Just 4 or 10% made landfall. Two did so as major hurricanes:

1893 “Midnight Hurricane:” Category 1 New York
1926 “Great Miami Hurricane:” Category 4 Florida and Category 3 Alabama
1938 “Great New England Hurricane:” Category 3 New York and Connecticut
2004 Frances: Category 2 Florida

The ensembles still suggest a far higher probability of East Coast landfall than would be the case with climatology. The consistent GEFS highlight greater landfall risk for the Southeast than the Virginia-New England region. My thinking that landfall is more likely than not and that the Southeast (GA-NC is probably at greatest risk) remains unchanged. But the event remains well enough in the future that there is considerable uncertainty with the 12z ECMWF solution being among the plausible options.
 

[bdgwx]

So I was confused by the statements that the HMON isn't run as an ocean coupled model. I mean, it stands for Hurricane Multi-scale Ocean-coupled Non-hydrostatic. So I did some poking around. Here is what I found.

Quote

The dynamical core of HMON is the Non-hydrostatic Multi-scale Model on a B grid (NMMB). It has 43 vertical levels with the model top fixed at 50 hPa. It includes vortex relocation, but has no data assimilation. It has been coupled to the HYCOM ocean model for EPAC and CPAC basins but runs uncoupled for the NATL basin. The HMON model runs on-demand with input provided by the National Hurricane Center (NHC) and consists of multiple movable two-way interactive nested grids that follow the projected path of a tropical system.

Source: http://nomads.ncep.noaa.gov/txt_descriptions/HMON_doc.shtml