Ask a Pro Met

[Mencken_Fan]

I'm not sure I agree that the answer is incorrect....many of our hottest days come with W/NW winds here in NYC metro, causing compressional warming off the Catskills/Poconos/NNJ hills. During July 2010, which was +4.8F at Central Park, quite a few of the torrid afternoons had flow from this direction. The Park was 94/71 on July 12th with a peak wind at 340 degrees; Central Park had a 4-day heat wave from 7/16-7/19, and those days all had W/NW winds for peak gusts. Often in summer, the hottest days come after cold fronts, which cause offshore flow and downsloping. Also, westerly winds tend to make it much warmer at night, limiting the effectiveness of radiational cooling.

I also think the poster is correct in asserting that the humid/swampy environment in Florida prevents the real heat from entering. NYC had dewpoints in the 40s on July 4th, 2010 when the temperature soared to 96F; these low dewpoints allow air to warm faster since its specific heat is lower than that of water vapor. It would be impossible to have Tds in the 40s during a Florida summer, so it takes more solar energy to warm the air the same amount.

Hello nzucker. I really shouldn't have posted here but it seemed no one was helping out the questioner so I tossed out some of the reasons for the difference between "northern" summer and Florida summer. (That Florida is a peninsula was so obvious I didn't bother mentioning that part.)

And speaking of those wicked hot NW winds in summer....we had that highly unusual (for July) wind direction today today in Wilmington, N.C. (on the coast at the bottom of N.C.) and guess what? Yep - our temperature soared to 102F! The intense heat caused a 180-degree shift in wind direction the next hour, with temps falling 5F pronto (to a more comfortable 97F, LOL.) It was our fourth day at or above the century mark this year....not at all typical of this coastal city. (And we had an unprecedented 3 days in May with 97F.)

[LithiaWx]

Why do the most intense hurricanes seem to peak out around 160mph? I know there are a few extreme exceptions but why does this happen. My first guess is they are limited by the water temps they form over. Is there a chart that shows max potential based on water temps? Hypothetically if we had ocean waters of 100+F would we have hurricanes of 250mph+? I do understand that storms weaken over colder waters but is the limiting factor of the most intense storms the cap of our ocean water temps of 90ish?

[phil882]

Why do the most intense hurricanes seem to peak out around 160mph? I know there are a few extreme exceptions but why does this happen. My first guess is they are limited by the water temps they form over. Is there a chart that shows max potential based on water temps? Hypothetically if we had ocean waters of 100+F would we have hurricanes of 250mph+? I do understand that storms weaken over colder waters but is the limiting factor of the most intense storms the cap of our ocean water temps of 90ish?

Here is the map you were looking for. You are primarily correct that most extremely powerful storms are limited by the SSTs they are under. Wilma was near its theoretical maximum potential intensity (MPI) when it bombed out in the Western Caribbean, and it would nearly be impossible to see a storm out in the far Atlantic get that intense because sea surface temperatures don't approach those values in the open Atlantic outside of the Caribbean and Gulf of Mexico. Its no coincidence that this is where we see our most intense tropical cyclones in the Atlantic Basin.

[LithiaWx]

Here is the map you were looking for. You are primarily correct that most extremely powerful storms are limited by the SSTs they are under. Wilma was near its theoretical maximum potential intensity (MPI) when it bombed out in the Western Caribbean, and it would nearly be impossible to see a storm out in the far Atlantic get that intense because sea surface temperatures don't approach those values in the open Atlantic outside of the Caribbean and Gulf of Mexico. Its no coincidence that this is where we see our most intense tropical cyclones in the Atlantic Basin.

Thanks, that was exactly what I was seeking.

[Uncle Bobby]

Can one of the more knowledgable mets explain how to tell what kind of tornado we are viewing when watching a U-Tube video.I guess we can all tell the multi-vortex monsters from a supercell, but tropical funnels, land spouts, water spouts, and how to tell which is which.  How high into the parent clouds structure they go.  Are gustnadoes and land spouts the same animal?If some pro-met was really motivated, they could even link U-Tubes of the various types of tornadoes.Bonus question- if tropical funnels generally form in low shear conditions, than a tornado in a hurricane's rain band wouldn't be a tropical funnel, no?

Disclaimer: I'm not a met, but I have 12 seasons of chasing under my belt. The following is meant to help, not be hard and fast rules that are non-breakable.

Ed, as I am fond of saying, no two storms are exactly alike, and no storm is exactly the same from one minute to the next. The same thing applies with YT vids, but here are some clues to help categorize between those various types of vortices:

Spouts:

I won't differentiate between landspouts and waterspouts as they are essentially the same animal.

The storm base into which the spout connects will often be fairly high as compared to a tornado from a mesocyclone, and the storm base may be lighter colored (i.e. not look so "angry").

The storm base may be somewhat wide and nondescript-looking (vs. being round and contracted)

Spouts are typically narrow from top to bottom, or "ropes".

As was stated, spouts can cause some serious damage, but they do not cause the same sort of damage as does a significant, violent tornado. If you watch a vid in which multiple buildings are exploding, it's not a landspout. If the debris near the ground doesn't seem to be moving violently, perhaps it is a spout.

Since the spout may be separated by some distance from any meso, there will probably not be vigorous lightning.

Tornadoes:

Tornadoes come in all shapes and sizes, but if it's a tornado there's a decent chance you can see rotation within the storm base as the whole mesocyclone spins.

The cloud base will often be quite dark and low to the ground.

If there are supercellular storm features present, such as an inflow band, and/or a clear slot (RFD), and/or a wall cloud, it's probably a tornado.

If the vid was shot with crops or grass in view, do you see a lot of swaying indicating strong inflow? That's a pretty decent indication that it's a tornado.

Gustnadoes:

Look for the shelf. If there's a big shelf cloud, it's a gustnado. Gustnadoes can sometimes be seen 2 and 3 at a time, too. You can also often see prodigous dust clouds blowing away from the storm in the same frame as a gustnado.

I hope that helps! Others can surely think of some other things.

Tornado:

http://www.youtube.com/watch?v=1MWnU6B7dTo

Landspout:

Waterspout:

http://www.youtube.com/watch?v=zcDWjI3QPE0

[saltysenior]

Outside of Florida, most Eastern cities are relatively near the Appalachian Mountains. Winds with a westerly component have been compressed and heated by "downsloping" off those mountains. This can generate significant heat (a bane in summer but a blessing in winter for those who dislike bitter cold Arctic air.)

Inland southern Florida has a lot of lake and swamp water which prevents "overheating" of the air. Inland air north of Florida sits over dry land; it can more easily heat up.

Northern cities are geared for heat; Miami is not.

with the sunshine and beaches and nitelife.....how come all the rich peoples houses are unoccupied .........come down for 2 weeks in aug and see for yourself if miami is not geared for heat

[AtticaFanatica]

User name lives up to the hype.

[patrick05]

got another question... is it really hard for tropical countries to reach 100F or more?? i look at the Philippines and they're always in the low to mid 90s..

if so why?? thanks

[SnowGoose69]

got another question... is it really hard for tropical countries to reach 100F or more?? i look at the Philippines and they're always in the low to mid 90s..

if so why?? thanks

Too much ocean influence and also frequent daily TS activity, the former though is more the reason. Most of these places have easterlies blowing all the time and ocean temps in the 80s so its virtually impossible to reach 100. San Juan has never hit 100, nor have some places in Florida though Key West and Fort Lauderdale have hit 100 in recent years for the first time.....an interesting note about reaching 100F is that Buffalo airport in NY has never hit 100 though Toronto has done it many times...the problem is a SW wind has a lake influence.

[Quixotic1]

Since spouts and tornadoes were brought up:

I swear I drove through a dust devil last week (Dallas) and saw another one just south of Waco today. Winds were light in both circumstances so it was kind of freaky. I don't remember seeing them ever before so I could be way off base. Is this a common phenomena, particularly in this area? I was wondering what conditions cause them since as near as I can tell, there's not much in the way of "cooler" air to work with.

[isohume]

Since spouts and tornadoes were brought up:

I swear I drove through a dust devil last week (Dallas) and saw another one just south of Waco today. Winds were light in both circumstances so it was kind of freaky. I don't remember seeing them ever before so I could be way off base. Is this a common phenomena, particularly in this area? I was wondering what conditions cause them since as near as I can tell, there's not much in the way of "cooler" air to work with.

Dust devils are not uncommon and they normally form in calm conditions or large scale subsidence zones. They are thermally driven and form when very warm air near the surface rises and stretches in response to small pockets of colder air moving overhead. This produces a secondary circulation...ie: air near the surface circulates as it converges near the dust devil. They maintain themselves by tapping into warm air ahead of their tracks, which themselves are maintained by the momentum of the llvl cyclonic field and friction near the surface. They can and usually do dissipate quickly if they stall too long and entrain cold air aloft into the funnel or move over an area of signif less sfc heating.

[Quixotic1]

Dust devils are not uncommon and they normally form in calm conditions or large scale subsidence zones. They are thermally driven and form when very warm air near the surface rises and stretches in response to small pockets of colder air moving overhead. This produces a secondary circulation...ie: air near the surface circulates as it converges near the dust devil. They maintain themselves by tapping into warm air ahead of their tracks, which themselves are maintained by the momentum of the cyclonic field and friction near the surface. They can and usually do dissipate quickly if they stall too long and entrain cold air aloft into the funnel or move over an area of signif less sfc heating.

Thanks!

[isohume]

Thanks!

No prob. Another thing regarding DD intensity. They are normally below 35 mph and can cause minor nuisance damage, if at all. However, sometimes they can reach severe criteria or even cat1 level. There have been cases of folks seriously injured or killed by dust devils. What an inglorious way to die. I think I'd rather get killed by hail.

[Quixotic1]

No prob. Another thing regarding DD intensity. They are normally below 35 mph and can cause minor nuisance damage, if at all. However, sometimes they can reach severe criteria or even cat1 level. There have been cases of folks seriously injured or killed by dust devils. What an inglorious way to die. I think I'd rather get killed by hail.

Funny you should mention that. The one I spotted near Waco was big. Easily visible from a mile away.

Sounds like a good topic: Ignominious Weather Related Deaths. Give me "hit by lightning while playing golf" for 500, Alex.

[isohume]

Funny you should mention that. The one I spotted near Waco was big. Easily visible from a mile away.

Sounds like a good topic: Ignominious Weather Related Deaths. Give me "hit by lightning while playing golf" for 500, Alex.

Yeah Texas and the SW in general get the strongest DDs. The semi-permanent ridge allows sfc lapse rates to go super-adiabatic, which of course increases upward acceleration and convergent cyclonic flow.

I'll take "killed by glare while driving for 250, Alex".

[metalicwx366]

Which hurricane/tropical storm produced the most tornadoes and what is the strongest tornado a hurricane/tropical has produced? I am very interested in hurricanes and the way tornadoes form from them.

[isohume]

Which hurricane/tropical storm produced the most tornadoes and what is the strongest tornado a hurricane/tropical has produced? I am very interested in hurricanes and the way tornadoes form from them.

When tropical systems move over land they experience increasing amounts of sfc friction. This leads to a significant increase in the directional and velocity shear and sets the stage for fairly easy tornadogenesis. The majority of these tornadoes are weaker and formed differently than dynamical supercell tors, however supercells can and do form within the spiral bands. True "tropical tors" are often short lived and are sometimes difficult to pick-up on the radar since there is generally no descending meso through a deep enough layer. They are basically "shear tors" tilting and stretching high amounts of available horizontal vorticity into the vertical. We've seen them reach EF2 strength across our CWFA, but the majority are EF0/1s.

As far as a tornado climatology associated with specific tropical systems, I'd check with NCDC. The climo buffs here may know some numbers off the top of their heads tho.

[AtticaFanatica]

As far as a tornado climatology associated with specific tropical systems, I'd check with NCDC. The climo buffs here may know some numbers off the top of their heads tho.

I could have sworn in the past 5 years or so, a climatological study of hurricane-induced tornadoes was published, but I can't find anything. All I see is case studies.

[isohume]

I could have sworn in the past 5 years or so, a climatological study of hurricane-induced tornadoes was published, but I can't find anything. All I see is case studies.

Yeah that would be hard data to find I imagine. If I had to find it, I'd get the tor and tropical data from NCDC for specific dates/times to make sure the events are related. It'd be good info to have around.

[Uncle Bobby]

I could be 100% wrong, but wasn't Ivan prolific at producing naders?

[isohume]

I could be 100% wrong, but wasn't Ivan prolific at producing naders?

Yeah I think it spawned about 120...but it could be more. It'd be interesting to see the actual climo on trop tors. The NHC may have those numbers.

[Uncle Bobby]

Yeah I think it spawned about 120...but it could be more. It'd be interesting to see the actual climo on trop tors. The NHC may have those numbers.

I once saw SRH around 1200 on SPC's mesoanalysis page. That might have been during Katrina, and IIRC that maxed out up around St Louis.

[isohume]

I once saw SRH around 1200 on SPC's mesoanalysis page. That might have been during Katrina, and IIRC that maxed out up around St Louis.

Yeah SRH and all the other shear indices can go "off the chart" when a tropical system moves over land, especially across the NE quadrant of course. Luckily, instability is normally low and relatively shallow with warm core systems.

[am19psu]

Dan Cecil is the guy you are looking for... here is the climatology...

http://journals.ametsoc.org/doi/abs/10.1175/2009MWR2896.1?journalCode=mwre

And his talk from Tuscon about forecasting them at landfall...

http://ams.confex.com/ams/29Hurricanes/recordingredirect.cgi/id/15008

[AtticaFanatica]

Dan Cecil is the guy you are looking for... here is the climatology...

http://journals.amet...ournalCode=mwre

Yes! Thanks, I was searching for hurricanes instead of tropical cyclones.

[LovintheWhiteFluff]

How accurate is the advanced dvorak technique when it comes to pressure and winds? It always seem like it's higher (sometimes by a lot) than the actual forecast given out by NHC or JTWC.

[hm8]

Dust devils are not uncommon and they normally form in calm conditions or large scale subsidence zones. They are thermally driven and form when very warm air near the surface rises and stretches in response to small pockets of colder air moving overhead. This produces a secondary circulation...ie: air near the surface circulates as it converges near the dust devil. They maintain themselves by tapping into warm air ahead of their tracks, which themselves are maintained by the momentum of the llvl cyclonic field and friction near the surface. They can and usually do dissipate quickly if they stall too long and entrain cold air aloft into the funnel or move over an area of signif less sfc heating.

So theoretically these could be often be occurring all the time in places with no dust or sand and just remain invisible and unnoticed?

Now that I think about it one time on a vacation out on the mountains there was a pretty large "snow devil" I'll call it on one of the ski trails...same deal here?

[isohume]

So theoretically these could be often be occurring all the time in places with no dust or sand and just remain invisible and unnoticed?

Now that I think about it one time on a vacation out on the mountains there was a pretty large "snow devil" I'll call it on one of the ski trails...same deal here?

Yeah, if there is not enough loose debris at the sfc then DD's will be invisible.

The "snow devils" you talk about are not produced by the same mechanism as DDs. Snowstorms often have gusty winds associated with them due to tight sfc pressure gradients and strong llvl jets responding to deformation and frontogenesis within the storm. This can, and often does, create deep and strong swirling winds at the sfc, especially across complex terrain like you've witnessed. They can maintain themselves and propagate like DDs, but they are a function of storm dynamics and not thermally driven like DDs.

[isohume]

How accurate is the advanced dvorak technique when it comes to pressure and winds? It always seem like it's higher (sometimes by a lot) than the actual forecast given out by NHC or JTWC.

The Advanced Dvorak Technique was designed to give objective guidance on TC intensity based on the orginal and subjective Dvorak Technique. The DT required a good amount of personal experience and time to gain reliable intensity estimates and could generally only be used in the later stages of a TC's development. The ADT uses computer sampling of a TC's cloud pattern and compares it to a statistical 10-year climatology before assigning a number. Unlike DT, the ADT can be applied in any stage of a TC's development. It has been found to be comparable in accuracy to the old DT employed by experienced forecatsers. However, just like any other guidance...the ADT is just another tool to help forecasters gain some measure of confidence when used and compared with other sources of guidance and real time data. It's overall accuracy is therefore subjective and depends on the scenario and forecaster utilizing it's output.

[River Card]

My question for you guys is...What implications could the SW drought have on the winter regarding strom tracks cutting into the great lakes? Could this be a player for the winter if the drought does not get busted. Thank you.