ATL: IRMA - Post-Tropical - Discussion

[KBBOCA]

A more zoomed in view of the Guadeloupe radar:
http://www.meteo.fr/temps/domtom/antill ... f_com.html

[MaineWeatherNut]

No, it's not. The cone of uncertainty is pretty wide at that point with Florida in the middle. If the 12z 's continue the eastward shift that the 6z's started this morning, the portion of the cone that is in the gulf now will be mostly gone by the 5pm update.

The Cone has nothing to do with Model runs. It has to do with the Official NHC Forecast track and then the cone is decided based on the amount of miles error there historically has been at each forecast point. So the only way the Cone will move out of the GoM is if the NHC moves their forecast.

If the NHC does not use the models to help determine their track, then why do they talk about the models in their forecast discussions? This makes no sense.

They do use the Models as Guidance. First of all they could keep their forecast as the western edge of the models. Also this far out they won't make huge jumps in their forecasts. They will gradually move their forecast one way or the other because the models will likely move back and forth for the next few days until we are closer to a US landfall.

All I am trying to say is the cone is in no way directly tied to the models it's tied to the NHC Official forecast.

[Hurrilurker]

Can someone please explain what this chart is and how to read it? I haven't seen them posted here much until this year. I guess it's some kind of pressure vs. dew point and temperature graph for a dropsonde and it means the core is stronger if the lines are straight up-down and closer together? But I don't understand it. And why are the vertical graph lines diagonal? Thanks in advance.

[CrazyC83]

000
URNT15 KNHC 051558
AF309 0811A IRMA HDOB 42 20170905
154930 1533N 05756W 6965 03150 0040 +095 +065 206045 047 049 003 00
155000 1535N 05756W 6970 03144 0042 +095 +067 203044 046 048 002 00
155030 1537N 05755W 6967 03145 0043 +092 +069 205045 046 048 003 00
155100 1539N 05755W 6964 03149 0047 +086 +077 207046 048 048 003 00
155130 1541N 05755W 6974 03133 0060 +078 //// 209046 050 048 005 01
155200 1543N 05754W 6963 03146 0060 +079 //// 213045 046 048 005 01
155230 1545N 05754W 6968 03134 0053 +085 //// 215046 052 046 005 01
155300 1547N 05753W 6967 03141 0034 +092 +089 218053 056 047 006 03
155330 1549N 05753W 6965 03139 //// +088 //// 212052 054 047 004 01
155400 1552N 05753W 6968 03132 //// +083 //// 209050 052 047 003 01
155430 1554N 05752W 6970 03130 0026 +090 +081 205050 055 047 002 00
155500 1556N 05752W 6965 03134 0031 +088 +083 204052 053 047 002 00
155530 1558N 05752W 6967 03132 0038 +084 +080 200054 054 045 005 00
155600 1600N 05752W 6966 03129 0032 +081 //// 200052 054 048 004 01
155630 1603N 05752W 6972 03121 0027 +086 //// 204051 053 049 005 01
155700 1605N 05752W 6968 03127 0024 +090 +086 199050 052 048 005 00
155730 1607N 05752W 6966 03123 0033 +083 //// 194052 054 049 005 01
155800 1609N 05752W 6967 03121 //// +079 //// 190054 056 051 002 01
155830 1611N 05753W 6965 03121 0032 +085 //// 197055 060 053 006 05
155900 1614N 05753W 6974 03109 0019 +087 +081 200060 061 053 002 00
$$
;

[Jimsot]

My goodness Anguilla looks like ground zero and will get the worst of Irma for hours.

This is the skeetobite 24 hour map showing the forecast for Irma from the 5 a.m. update when Irma was still a Cat 4.

http://www.skeetobiteweather.com/

Shows quite well which Islands will be within the Hurricane force vs. Tropical Storm winds:

[Sanibel]

GFS hits Ft Lauderdale with a category 5...2nd run in a row now...

[Vdogg]

GFS comes east again, grazes east Florida with eyewall. Looks like a Carolinas landfall coming up.

[gatorcane]

GFS hits Ft Lauderdale with a category 5...2nd run in a row now...

Eye passes just east of SE Florida but enough to put SE Florida in western eye wall. Hopefully this is start of a trend east away from SE Florida though the Bahamas would be in trouble.

[ObsessedMiami]

The panic in S Fla on Wednesday-Thursday (ish) is going to be extreme if something doesn't knock Irma down soon. Evacuation will soon be an impossibility for most people.

So when does Miami Dade and Broward begin the Emergency Operations centers and announce evacuation schedules?

[Evil Jeremy]

The panic in S Fla on Wednesday-Thursday (ish) is going to be extreme if something doesn't knock Irma down soon. Evacuation will soon be an impossibility for most people.

So when does Miami Dade and Broward begin the Emergency Operations centers and announce evacuation schedules?

Emergency centers already rolling.

[CrazyC83]

000
URNT15 KNHC 051608
AF309 0811A IRMA HDOB 43 20170905
155930 1616N 05753W 6968 03113 0035 +073 //// 200059 061 055 005 01
160000 1618N 05753W 6967 03107 0028 +079 //// 188067 072 055 005 01
160030 1620N 05753W 6974 03096 0003 +077 //// 188067 072 056 003 01
160100 1623N 05754W 6969 03099 9995 +090 +079 189068 069 056 002 00
160130 1625N 05754W 6964 03100 9998 +085 +080 185069 070 057 003 00
160200 1627N 05754W 6969 03092 0031 +073 +073 182071 072 058 007 00
160230 1630N 05754W 6966 03092 0024 +073 //// 180072 073 058 006 01
160300 1632N 05754W 6969 03087 0015 +079 +079 182075 077 056 007 03
160330 1635N 05755W 6953 03105 0019 +079 +079 178074 077 056 011 00
160400 1637N 05755W 6979 03068 9995 +083 +082 185072 074 056 011 00
160430 1639N 05755W 6967 03084 0003 +083 +083 184074 076 053 013 03
160500 1642N 05755W 6971 03082 0013 +082 +082 174073 076 053 009 00
160530 1644N 05756W 6963 03083 0003 +084 +084 169071 072 052 016 03
160600 1647N 05756W 6971 03083 9999 +088 +088 168072 075 056 007 00
160630 1649N 05756W 6967 03076 9997 +080 +080 169074 076 055 008 00
160700 1651N 05756W 6968 03076 9995 +077 //// 168077 079 054 008 01
160730 1654N 05756W 6965 03078 9981 +078 //// 169081 082 054 003 01
160800 1656N 05757W 6966 03077 9979 +078 //// 167078 081 054 004 01
160830 1659N 05757W 6962 03084 9992 +077 //// 161082 084 054 005 01
160900 1701N 05757W 6971 03075 0000 +074 +073 157085 086 054 003 00
$$
;

[tolakram]

If the NHC does not use the models to help determine their track, then why do they talk about the models in their forecast discussions? This makes no sense.

They use the models to help make their forecast, but their forecast and the cone of error that surrounds it is fixed year to year.

Here is their explanation: http://www.nhc.noaa.gov/aboutcone.shtml

[Chris_in_Tampa]

Radar loop from NOAA hurricane hunters earlier:
https://www.youtube.com/watch?v=0-hT4F885ck
3:50am to 9:35am AST

[CrazyC83]

000
URNT15 KNHC 051619
AF309 0811A IRMA HDOB 44 20170905
160930 1703N 05757W 6965 03084 9991 +078 //// 152086 086 053 005 01
161000 1706N 05758W 6971 03077 0006 +073 +073 151084 086 052 009 00
161030 1708N 05758W 6971 03076 0010 +073 //// 148082 084 056 009 01
161100 1711N 05758W 6968 03086 9991 +080 +080 148085 086 055 003 01
161130 1713N 05758W 6967 03089 9992 +080 +078 145081 083 056 005 00
161200 1715N 05758W 6973 03084 0002 +081 +081 145088 095 056 006 03
161230 1718N 05759W 6971 03094 0021 +079 +079 144088 096 055 009 00
161300 1720N 05759W 6963 03101 0014 +075 +075 139085 086 052 006 00
161330 1722N 05759W 6970 03095 0008 +079 +078 137084 085 054 005 00
161400 1725N 05759W 6966 03103 0013 +076 +074 135082 084 054 004 00
161430 1727N 05800W 6968 03101 0004 +085 +076 133079 081 055 005 00
161500 1729N 05800W 6971 03100 0018 +078 +077 133079 079 054 004 00
161530 1731N 05800W 6968 03106 0019 +083 +083 131078 079 054 009 03
161600 1734N 05800W 6968 03104 0027 +085 +085 130079 082 058 014 00
161630 1736N 05800W 6976 03103 0040 +082 //// 131077 079 049 028 05
161700 1738N 05801W 6963 03112 //// +073 //// 132082 083 /// /// 05
161730 1738N 05804W 6962 03109 //// +075 //// 128076 081 /// /// 05
161800 1737N 05805W 6973 03089 0023 +085 //// 124075 076 055 017 05
161830 1735N 05806W 6975 03087 0020 +085 //// 125076 077 058 011 01
161900 1734N 05807W 6966 03104 0007 +081 +081 127078 080 056 006 00
$$
;

[AutoPenalti]

The panic in S Fla on Wednesday-Thursday (ish) is going to be extreme if something doesn't knock Irma down soon. Evacuation will soon be an impossibility for most people.

So when does Miami Dade and Broward begin the Emergency Operations centers and announce evacuation schedules?

Evacuations I would think probably by Thursday.

[Stormcenter]

So what happens when 95L develops into a storm in the SW Gulf, how does that affect Irma if at all?

[Buck]

Every time I think Irma is going to start an EWC the last 18-24 hours, it doesn't. It's presentation now is just about the most impressive I've ever seen. Incredible.

[Michele B]

Sometimes when it rains it pours. notice the track for newly designated Jose crosses Irma's path as a category 2 storm. Imagine if there was a landmass at that point...you'd feel really unlucky. I guess the point is that just because a spot has recently been hit doesn't mean it's off the hook going forward. thank goodness it's in the middle of the ocean.

I posted, I think on Models thread yesterday (I think I forgot where I was! Ooops) a link that shows Jose is supposed to go North, LOOP around and come right up behind Irma - hitting all the same places!

DANG!! Enough is enough, already! Those poor people on the islands....

[Shuriken]

"...fluctuations in intensity are likely to occur as eyewall replacement cycles take place...." (The NHC, as its forecast slowly bleeds off strength from Irma 180>175>etc. prior to passage north of Puerto Rico)

-- This makes absolutely no sense to me. They're not predicting an increase in shear or other mitigating factor, and the Virgin Islands present no disruptive profile to the wind. So, why expect weakening?

Irma is now a steady-state, top-ended hurricane with an almost annular-looking core. Allen, David, Mitch, and Isabel showed that such storms can and do supercruise at cat-5 until they approach land (or, in the case of Isabel, plow through howling shear).

[psyclone]

Recent runs show how just 2 or 3 degrees of longitude can make a huge difference (make or break) in term of impacts. The NHC doesn't have the luxury of lurching the track around in the extended outlooks every 6 hours. If an easterly trend develops you will see a gradual shift of the end point over multiple forecast cycles.