ATL: IRMA - Post-Tropical - Discussion

[Blown Away]

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.

The GFS has just W of N from below Miami all the way to inland Carolinas....

[tropicwatch]

Man this thing is a monster.
http://rammb-slider.cira.colostate.edu/?sat=goes-16&sec=full_disk&x=16511.3193359375&y=7392&z=3&im=12&ts=1&st=0&et=0&speed=130&motion=loop&map=1&lat=0&p%5B0%5D=21&opacity%5B0%5D=1&hidden%5B0%5D=0&pause=0&slider=-1&hide_controls=0&mouse_draw=0&s=rammb-slider

[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?

Evacuations I would think probably by Thursday.

They would have to start tomorrow. If the worst case scenario unfolds and you have a major hurricane riding up the peninsula, coastal evacuations could extend north of Lake O. People from Miami will be fighting to go North with people hundreds of miles already to their North, if they wait until Thursday. The most southern Floridians would need to hit the road tomorrow to avoid a traffic calamity. Thursday will be the masses, and Friday the last-minute ditchers.

[psyclone]

"...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).

Hurricanes rarely maintain a maxed out intensity for long...at this point it's reasonable to expect some fluctuations in intensity. it will be interesting to see if downsloping off the greater Antilles has an adverse impact on the system when it reaches that longitude.

[ronyan]

Wunderground forecast for the island of Anguilla (UK) tonight: Heavy Rain/Wind. High 86F. SSW winds at 145 to 160 mph, decreasing to 80 to 100 mph.

[nativefloridian]

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

Evacuations I would think probably by Thursday.

They would have to start tomorrow. If the worst case scenario unfolds and you have a major hurricane riding up the peninsula, coastal evacuations could extend north of Lake O. People from Miami will be fighting to go North with people hundreds of miles already to their North, if they wait until Thursday. The most southern Floridians would need to hit the road tomorrow to avoid a traffic calamity. Thursday will be the masses, and Friday the last-minute ditchers.

According to the local news here in Miami, mandatory evacuations will begin in Monroe County (Keys) tomorrow at sunrise; also their government offices and schools will be closed beginning tomorrow. Since I'm a Miami-Dade County employee, I'm waiting right now for the Mayor's live press conference on, I suppose, when/what actions will be taken in Dade County.

[SouthFLTropics]

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 have firsthand experience of this point being proven 3 weeks apart from each other in 2004 when Frances and Jeanne came a calling on my doorstep.

[Kazmit]

Probably the best satellite presentation I've ever seen of an Atlantic storm. Image is not current.

[Cunxi Huang]

SFMR 160 KT...

163330 1702N 05841W 6961 02668 9504 +115 +115 139132 141 160 046 00
163400 1701N 05842W 6962 02616 //// +109 //// 137121 133 160 024 05

[tolakram]

Visible loop, takes a while to load.

http://rammb.cira.colostate.edu/ramsdis/online/loop.asp?data_folder=goes-16/mesoscale_01_band_02_sector_05&width=1000&height=1000&number_of_images_to_display=40&loop_speed_ms=80

[tolakram]

[Extratropical94]

https://i.imgur.com/VvsYXWl.png

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.

It indeed is a temperature/dew point vs pressure (T-p) graph for a dropsonde with wind barbs added at the side. The dots resemble the heights where temperature measurements were made. To derive the temperature and dewpoint at a certain height, just go from a point on the red or green graph to the bottom scale by moving parallel to the dashed slanted lines.

When the green line (dew point) and the red line (temperature) are close together, that simply means that the air is saturated with water vapor and the relative humidity is near 100%. This is common within clouds, fog or areas where humid air is rising and the water is about to condensate, like for example in the eyewall of a hurricane. In the eye the air is typically sinking which forces adiabatic heating and the humidity decreases a little. That's why you see the green and red lines separated from each other in a center dropsonde diagram.

I think here the diagrams are mainly used to visualize the wind speeds at different heights (which are also shown in the table on the right, together with all the 'decoded' temp and dew point data). Evaluating the strength of the core is easier with other tools, as these graphs do only show absolute temperatures, not the temperature differences between the core and the ambient air at the same level.

T-p diagrams do often have slanted vertical lines for temperature (those diagrams are called "skew-T"-diagrams). Two reasons for that. First, you can set the inclination of the isotherms (dashed lines of constant temperature) to a specific value to make a certain vertical temp profile appear as a straight vertical line. By doing that you can for example make assumptions about the stability of the atmosphere by just looking of the inclination of the T-line. Second, you need less space. There is no need for a +30°C line at 50000 feet or a -90°C line at the surface. Basically it avoids temperature curves that get too far out to the sides.

[znel52]

160kt SFMR.....

[CrazyC83]

000
URNT15 KNHC 051639
AF309 0811A IRMA HDOB 46 20170905
162930 1710N 05832W 6968 02929 9836 +074 +074 131128 130 092 030 00
163000 1709N 05833W 6965 02915 9817 +078 +078 130132 134 098 052 00
163030 1708N 05835W 6960 02902 9775 +095 +095 136128 132 110 029 00
163100 1707N 05836W 6979 02837 9735 +099 +099 136129 130 116 014 00
163130 1706N 05837W 6969 02825 9698 +099 +099 134135 137 121 021 03
163200 1705N 05838W 6962 02797 9664 +098 +098 133142 143 122 027 03
163230 1704N 05839W 6965 02754 9623 +099 +099 134145 150 136 075 00
163300 1703N 05840W 6973 02711 9573 +106 +106 138145 151 147 066 00
163330 1702N 05841W 6961 02668 9504 +115 +115 139132 141 160 046 00
163400 1701N 05842W 6962 02616 //// +109 //// 137121 133 160 024 05
163430 1700N 05843W 6956 02574 9331 +145 +140 140102 115 /// /// 03
163500 1659N 05844W 6979 02525 9293 +174 +146 143085 093 121 001 03
163530 1658N 05845W 6957 02529 9262 +179 +147 148070 081 082 001 03
163600 1657N 05846W 6976 02491 9240 +192 +141 150048 063 067 000 00
163630 1656N 05848W 6970 02487 9240 +179 +139 155037 043 058 001 03
163700 1655N 05849W 6963 02490 9235 +175 +133 162024 034 040 003 00
163730 1654N 05851W 6961 02491 9235 +174 +131 153010 018 030 001 00
163800 1653N 05853W 6965 02485 9237 +172 +127 055002 005 026 000 00
163830 1652N 05854W 6967 02484 9239 +173 +126 332010 014 029 000 00
163900 1652N 05856W 6965 02490 9247 +169 +128 321015 016 029 001 03
$$
;

151 kt FL, 160 kt SFMR - whoa!!!!!!!

[Yellow Evan]

Why is the SFMR winds so much higher than FL all of a sudden? I'd expect that in a pinhole eye storm but not for a large eye storm.

[znel52]

Probably the best satellite presentation I've ever seen of an Atlantic storm. Image is not current.

I'd give it to Gilbert but this is right there with it. Unbelievable!

[SouthDadeFish]

SFMR readings are at WTF levels. Even stronger than flight-level winds. Not sure what the NHC will do with them. Maybe they found a mesovortex?

[dukeblue219]

SFMR 160 KT...

163330 1702N 05841W 6961 02668 9504 +115 +115 139132 141 160 046 00
163400 1701N 05842W 6962 02616 //// +109 //// 137121 133 160 024 05

Unbelievable. I wonder if we'll hear anything about this morning's NOAA and USAF flights and the conditions they encountered. The USAF crew in particular has been in the NE eyewall three times today, each time getting cat5+ measurements.

[TheStormExpert]

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 have firsthand experience of this point being proven 3 weeks apart from each other in 2004 when Frances and Jeanne came a calling on my doorstep.

The "when it rains it pour" statement can apply to the fact that we could be seeing back-to-back major hurricane landfalls in the U.S. after going nearly 12 years without one.

[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).

Hurricanes rarely maintain a maxed out intensity for long...at this point it's reasonable to expect some fluctuations in intensity. it will be interesting to see if downsloping off the greater Antilles has an adverse impact on the system when it reaches that longitude.

But we're not talking about hurricanes in general; we're talking about specific hurricanes in this particular situation: top-ended ones (not pinholes). Go look at Allen's track: if it weren't for all the Greater Antilles is brushed up against threading the needle, that storm would have been a cat-5 for four solid days.

If the ocean heat content under Iram presently supports a top-ended intensity of 180mph, then the higher heat content west of the storm does not suggest weakening is in the future. If the storm hits a big, mountainous island, it will weaken. If it runs into shear, it will weaken. But on the forecast track they're projecting, there is no logical reason for it to weaken in the next 24hours.