ATL: ISAAC - Post-Tropical - Discussion

[ozonepete]

If it doesn't go to hurricane soon I'll have to reduce my category 3 prediction to 2. Time to fess-up this is still fatally dry on the east side and hindering development as a permanent feature.

Fatal is a strong word.

[Wthrman13]

Sorry for the elementary school question, but is this good or bad? What is CAPE and how does it affect storms?

CAPE stands for "Convective Available Potential Energy". It's a measure of the potential energy available in a vertical column of the atmosphere for a rising air parcel to accelerate. In other words, it's a measure of the potential strength of a thunderstorm updraft. The higher the CAPE, the stronger the updraft, all other things being equal. Roughly, values of 0-1000 J/kg are considered low, 1000-3000 J/kg or so are moderate and 3000+ are high. Typically, because of less surface heating over the water, CAPE is lower over the ocean.

In any case, TC's are driven more by air-sea interaction than by atmospheric CAPE, although the latter does play a role.

Oh, and never be sorry for an elementary question!

[uhvjaguars22]

being on the central texas coast this thing would have to come due west and even for houston not likely i wouldnt think but who knows with this weird storm

[nashrobertsx]

what is COL

[southerngale]

being on the central texas coast this thing would have to come due west and even for houston not likely i wouldnt think but who knows with this weird storm

Actually, due west would put it around Brownsville.

[ozonepete]

I personally wouldn't pay much attention to the CAPE analyses out over the Gulf. They are subject to large errors due to lack of data. Essentially what you are seeing is almost purely the short-range RAP forecast that serves as the background for the SPC mesoanalysis.

I would pay attention to what he says, guys. As he said, those measurements are very rough and very suspect. CAPE is available potential energy, not actual energy. So you can have very high CAPE and very little convection - for example air can be very dry and still have high lapse rates and thus high CAPE, but just looking at CAPE wouldn't show that.

[otowntiger]

Had a decent squall move through Orlando this morning about 5:30, measuring 38mph on my Davis weather station anemometer. As of early this morning we've gotten just over a half inch from this system and no significant wind other that that one gust I recorded. Although its still raining here pretty steady that should be considerably higher by the end of the day. The effects over here have certainly been less than was originally forecast. That obviously is due to the storm's lack of intensification (up til now) and moving further away from us at the same time. I mention this because I still think it's pretty impressive that we are 300 miles away and can still get that much weather while its moving away.

[Nikki]

I am by no means arguing with the NHC nor am I poking fun at them, I am just trying to understand, so maybe someone can help me. Is Isaac moving WNW or NW?


...ISAAC MOVING WEST-NORTHWESTWARD OVER THE EASTERN GULF OF
MEXICO...POSES SIGNIFICANT STORM SURGE THREAT TO THE NORTHERN GULF
COAST...

SUMMARY OF 1000 AM CDT...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...26.1N 85.3W
ABOUT 250 MI...400 KM S OF APALACHICOLA FLORIDA
ABOUT 310 MI...500 KM SE OF THE MOUTH OF THE MISSISSIPPI RIVER
MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H
PRESENT MOVEMENT...NW OR 305 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...988 MB...29.18 INCHES

[uhvjaguars22]

southerngale do u think this is still possible to stay weak and head for texas, im thinking of another relocation to the west just a tad

[Portastorm]

I am by no means arguing with the NHC nor am I poking fun at them, I am just trying to understand, so maybe someone can help me. Is Isaac moving WNW or NW?


...ISAAC MOVING WEST-NORTHWESTWARD OVER THE EASTERN GULF OF
MEXICO...POSES SIGNIFICANT STORM SURGE THREAT TO THE NORTHERN GULF
COAST...

SUMMARY OF 1000 AM CDT...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...26.1N 85.3W
ABOUT 250 MI...400 KM S OF APALACHICOLA FLORIDA
ABOUT 310 MI...500 KM SE OF THE MOUTH OF THE MISSISSIPPI RIVER
MAXIMUM SUSTAINED WINDS...65 MPH...100 KM/H
PRESENT MOVEMENT...NW OR 305 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...988 MB...29.18 INCHES

Technically movement between 303.75 and 326.25 degrees is considered northwest.

[tolakram]

I am by no means arguing with the NHC nor am I poking fun at them, I am just trying to understand, so maybe someone can help me. Is Isaac moving WNW or NW?

Isaac is moving WNW until the NHC says it isn't. Either we have to stick with them or take your pick at the best met or amateur analysis and go with that. I'd stick to the NHC.

[southerngale]

southerngale do u think this is still possible to stay weak and head for texas, im thinking of another relocation to the west just a tad

I never thought it was coming to Texas. I guess it's possible, but seems highly unlikely, IMO.

[jinftl]

I could see the hurricane warning for the panhandle being lowered to tropical storm warning later...they are not in the forecast cone any longer and the forecast radius of hurricane force winds based on current forecast is 30 miles to the ne and se of the center. Panhandle will see t.s. conditions unless a major jump north happens.

Also note that part of sw LA in the cone has only a tropical storm watch in effect by comparison. I could see that becoming a ts warning later...

[GCANE]

That is almost an increase of 60%. That is substantial.

Sorry for the elementary school question, but is this good or bad? What is CAPE and how does it affect storms?

http://en.wikipedia.org/wiki/Convective ... ial_energy

It is an indication of how rapidly a cu-nim can rise. I am trying to correlate it to overshooting tops and hot towers.

OTs and hot towers in turn warm the core up by latent heating which strengthens a TC.

[Ellsey]

I am by no means arguing with the NHC nor am I poking fun at them, I am just trying to understand, so maybe someone can help me. Is Isaac moving WNW or NW?

Isaac is moving WNW until the NHC says it isn't. Either we have to stick with them or take your pick at the best met or amateur analysis and go with that. I'd stick to the NHC.

The problem is NHC said both. I'm wondering if they just used old stuff and forgot to switch the first WNW to NW. Or maybe just got excited typing Ws....

[Portastorm]

I am by no means arguing with the NHC nor am I poking fun at them, I am just trying to understand, so maybe someone can help me. Is Isaac moving WNW or NW?

Isaac is moving WNW until the NHC says it isn't. Either we have to stick with them or take your pick at the best met or amateur analysis and go with that. I'd stick to the NHC.

The problem is NHC said both. I'm wondering if they just used old stuff and forgot to switch the first WNW to NW. Or maybe just got excited typing Ws....

Please see what I posted above. NHC says movement at 305 degrees. That is considered "northwest." Here is a handy-dandy chart:

http://climate.umn.edu/snow_fence/Components/winddirectionanddegreeswithouttable3.htm

[ROCK]

Boy.. I am sure glad the Florida folks didnt get hit to bad...it was only a few days ago this was going to smack them pretty hard up the spine or into Miami....Dodged another bullet...

[Nikki]

I am by no means arguing with the NHC nor am I poking fun at them, I am just trying to understand, so maybe someone can help me. Is Isaac moving WNW or NW?

Isaac is moving WNW until the NHC says it isn't. Either we have to stick with them or take your pick at the best met or amateur analysis and go with that. I'd stick to the NHC.

The problem is NHC said both. I'm wondering if they just used old stuff and forgot to switch the first WNW to NW. Or maybe just got excited typing Ws....

That is where I got confused. I am no weather genius and am just trying to learn Thank you everyone for the responses!!

[PTrackerLA]

Appears to have moved more westerly recently probably due to convective burst.

[Sanibel]

Dvorak is best it's ever been in my opinion.