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A quiet day in the tropics

By: Dr. Jeff Masters, 1:18 PM GMT on July 07, 2006

An area of disturbed weather in the western Caribbean is expected to move onshore the Yucatan Peninsula tonight with no development. We'll have to watch this disturbance when it crosses into the southern Gulf of Mexico Saturday. The computer models are not predicting development, though.

The area of disturbed weather south of the Carolinas is associated with a front, and no tropical development is expected. The computer models continue to show an area of low pressure developing in the vicinity of this front tonight. It is now apparent that this low will be extratropical, since it is expected to form where there is a strong front with contrasting temperatures on either side. The low is expected to move north and bring strong winds to the Outer Banks of North Carolina on Saturday, and possibly to Cape Cod on Sunday. Elsewhere in the tropics, there is nothing of note today.

Figure 1. Current weather map for the Southeast U.S. shows a front and plenty of rain south of the Carolinas.

Tropical, subtropical, extratropical?
It is often difficult to tell from looking at forecast model data this time of year whether a low that is expected to develop near the U.S. coast will be tropical, subtropical, or extratropical. The difference is important, since tropical systems have the potential to quickly grow into hurricanes, while extratropical or subtropical storms do not. So, here's a quick meteorology lesson on the differences. We talk about three main types of large-scale storms (also called cyclones):

Tropical cyclones. These include tropical depressions, tropical storms, and hurricanes (which are called typhoons the Western Pacific). Tropical cyclones have warm air at their core, and derive their energy from the "latent heat" released when water vapor that has evaporated from warm ocean waters condenses into liquid water. Tropical cyclones form only over waters of at least 80 F (26 C). One does not find warm fronts or cold fronts associated with a tropical cyclone. Tropical cyclones regularly become extratropical cyclones when they get close enough to the pole to get caught up in a front.

Extratropical cyclones. These include blizzards, Nor'easters, and the ordinary low pressure systems that give the continents at mid-latitudes much of their precipitation. Extratropical cyclones have cold air at their core, and derive their energy from the release of potential energy when cold and warm air masses interact. These storms always have one or more fronts connected to them, and can occur over land or ocean. In winter, extratropical cyclones over water can grow as strong as a Category 3 hurricane.

Subtropical cyclones. These storms occur over the oceans, and are a mix between a tropical cyclone and an extratropical cyclone. Subtropical cyclones get their energy from latent heat like tropical cyclones, and from potential energy of contrasting air masses, like extratropical cyclones. A subtropical cyclone typically has an exposed center of circulation, with very heavy thunderstorm activity in a band removed at least 100 miles from the center of circulation. The difference between a subtropical storm and a tropical storm is not that important as far as the winds they can generate. It is common for an extratropical cyclone to form over cold waters, move Equatorward over warmer waters, and gradually acquire a warm core and enough deep thunderstorm activity to be classified as a subtropical storm. Eventually, many of these will become full-fledged tropical storms if the deep thunderstorm activity can move all the way to the center, and the core becomes warm from the surface to the upper atmosphere. Subtropical cyclones very rarely attain hurricane strength.

I'll be back tomorrow with an update on the tropics. On Monday I plan to discuss the long range outlook for July, and when we might start to see some action in the Atlantic. I really don't see much to be concerned about in the next few days, and the long range outlook--so far--is for typical July weather. This is not the Hurricane Season of 2005!

Jeff Masters

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

Posted By: jphurricane2006 at 6:12 AM GMT on July 08, 2006.
can bursts of convection be created by divergence in the upper level winds
JP - Defintely, the divergence at the upper levels pulls up air closer to the surface, so it can create some heavy convection. A lot of these short lived areas of convection in the tropics are caused by upper-level divergence.

Another cause of convection is low-level convergence, where winds at the surface are converging which causes rising air and convection.

Not only that the Army Corps of Engineers uses (used) a Cat 3 "standard project hurricane" from 1950 to establish levee guidelines here in New Orleans. I don't know why Katrina was downgraded to a 3,because Mississippi was flattened so it was definitely a 4 in Gulfport, whereas maybe near my house the winds were not all that bad I have been in worse but even so it sounded like the devil was up there.
If that's our Yucatan blob already in BoC, then it's not such a big deal unless it stalls and strengthens. At the rate it's going and with the front coming off the gulf, worst case is maybe a weak TS for South Texas.

It's much farther West than NOGAPS forecast Wednesday night too. Overall good news I'd say. That almost definitely keeps it out of the eastern gulf and keeps it from being too interesting.
Actually anything that makes it north of puerto rico will be forced almost on westward path because the building high.
To be Honest jbhurricane2006 Dry air and high Surface Pressures are Dominateing the Atalntic right now in the region were these intence monsters can get going. In My opinion even The Potential for a Coastal Low Pressure seems Very low at the moment,besides july is usually a pretty quiet month,I think we will be seeing a more Typical active hurricane season that should see the potential for development go up towards the end of the month.
I think that there is a high building over the wave and that the high will build west with the wave over time, so the shear will lessen as the wave progesses. Climatologically, it is early for a Cape Verde system to form yet, so I am cautious right now as to whether it will develop, but it certainly bears watching over the next few days. A lot depends on whether the ULL north of P.R. moves farthr north or NW and weakens.

I am off to take another look at the loops and models, check back soon.
it better begin on a WNW path soon or it will run into central america.
Its got some good spin to it but it needs to get going on a WNW path or we can kiss this wave bye as it will run into central america.
jphurricane2006 i dont think there are any ship reports outthere at the current time.
An example of a July Cape Verde system was Hurricane Bertha (1996). I remember they ordered evacuation of the FL east coast barrier island where I live, but I lingered and decided to stay after it turned north. The sun stayed out as we were under the subsidence, but the 18 sec period swells that were crashing on the beach while it was passing offshore were the largest I had ever seen on the beach in Florida, although the tide didn't rise nearly as much as when Floyd passed by much closer offshore.
Guys iam going to bed i leave you with a IR image of Hurricane Dennis in July 2005.

Photobucket - Video and Image Hosting
jphurricane - See my answer above. Also, there is a large upper-level high currently over the wave and that is currently a favorable environment for the wave. Note that the flow between that Upper-level high and the ULL north of Puerto Rico is pulling a stream of strong shearing upper level winds between the two systems. For the wave to survive and strengthen, that upper-level high needs to move in tandem towards the west above the wave, and the ULL needs to move north and weaken. Also there is a pretty good rule of thumb that if a system is to survive the Eastern Caribbean, it should be a named storm before it crossed the Lesser Antilles. If the wave curves north of the Lesser Antilles, the conditions will most likely will be more hostile for development. Crossing over or too close to Hispaniola also would not be conducive for development, as the large mountains tend to shear systems apart. So a lot depends on the track, and whether shear currently along the track lessens. Right now, it looks like a healthy large open wave, with some ULH support developing over it. Another day or two should tell us a lot more.
OK, goodnight all!
I agree with ur thoughts guygee the track of this wave will be important.also the rule of thumb u mentioned is 100% right,most if the time it has to be a named storm before it crosses the Lesser Antilles or the chances are this wave wont amount to much.It will just go POOF....
I hope we don't see anything like Dennis this July, hurricane23! If I remember, it weaked somewhat before it landfall, but that is one impressive looking hurricane in the image above.
I'm having trouble sleeping tonight, but i think it is time to give it a try. Talk to you again soon!
Well to put an exclamation point on the night (morning, actually), the Melbourne early morning AFD specified which system was forecast to be over FL by this Wednesday, and it is NOT the wave over the central Atlantic, but rather the ULL just North of Puerto Rico. Here is the excerpt:

219 AM EDT SAT JUL 8 2006
the weather channel made it a point to talk about the wave in the atlantic. that is something they are watching..it has some rotation and convection is steady
Been watching storms since I was a kid (longer ago than I want to admit). All I have to say right now is, there is a lot more activity going on out in the Atlantic in July than I've seen.
526. IKE
I think this hurricane season might need some Viagra. I know it's early, but so far it has been a real yawner........

527. IKE
Dam...that is an impressive IR picture of Dennis. Hard to believe there can be that much difference between one year to the next. Last year we were up to Emily by now.......
Ike for someone on the MS Gulf Coast that went through Hurricane Katrina all I can say is...THANK GOD
lets just hope it stays this way!!
530. IKE
Amen .......

I agree....

I'm glad......
531. IKE
Katrina was just incredible. I think NO and the Mississippi coast will be okay this year..
It is hard to believe this time last year Dennis was about to enter the Gulf..and Emily was also out there..and today nothing!!
I hope youre right Ike..but I think youre right..the pattern this year is different from last year
534. IKE
The difference in one year...2005 to now...how does anyone scientifically predict that???

It's impossible.
I know..do you think will see up to 18 named storms this year with the way the season started off..I know typically June and July isn't the busiest months..but what do you think?
536. IKE
I've looked at the GFS models and time after time...there's nothing. Even now it shows only the tropical wave cruising into eastern Florida and keeps it as a rainmaker. Other then that...it looks like a fall weather pattern...a cold front down to Tampa in July...OMG!
I know thats so unusual...its hard to believe there is a trough across the south and east in early July
538. IKE
I don't think they'll be that many storms...but that's just an opinion....I'll say 13-14 storms...and that might be a stretch.
539. IKE
Im in the Florida panhandle and there's just no rain to speak of this summer...one of the driest on record....half the normal rain total...
540. IKE
Be back in a little bit......
It might be possible this year could end up like 2004 where it started off in early August then exploded after that..that year ended up with 14 named storms
Same here on the MS Coast Ike..im north of Gulfport and here at my house i've only had 18.79" for the year..normally around early July its around 32.00"
In my un-expert opinion, the Belize Blob will become a tropical cyclone.

In the Pacific.
It was dry here slightly North of Houston from late last summer (even Rita only dropped about an inch of rain) right through until about Memorial Day.

In the last 6 weeks, the drought has pretty much gone.

After I wake back up, the lawn will need a mowin'
Did Belize get relocated ? It can't possibly cross that terrain!
Any surface circulation would get disrupted over hilly terrain, (not that there ever was a surface circulation) but any mid-level circulation might hang on, along with the higher heat/moisture until it reaches the East Pac, where the GFS is still suggesting a mini-development burst.

Hey, its July, it is supposed to be slow in the Atlantic.
If it don't stop rainin' here in Fort Myers this weekend I'll need a bush hog to mow my yard.
Back to bed. Still basically dark here, which is a noticeable change from just 2 weeks ago, as the long slog towards winter has begun.

I remember a cold fromt in mid august 2004 that came thr here in pcola and I had to take a jacket to baseball game.that is the day bonnie was pushed into big bend area and charley was pushed into sw fla 12 hours later.I thought then that this may be the end of the 04 season because I had never seen such a strong front in august on the gulf coast. Boy was I wrong that seemed to be the spark for frances, ivan and jeanne.this maybe Like 2004 and this front maybe the spark to start the real hurricane season and the wave at 35 -40 west is looking a lot better this morning.
N. of Puerto rico is gathering moisture along with the circulation, Keep an eye on it.
I can't remember the last time I saw a cold front dip this far south in July! Very strange.
552. PBG00
Mornin all...Waking up to more rain..in for some severe storms this afternoon..thanks to our front.
chef, i see that train still running through your backyard. up here, currently too many scattered storms roaming around to venture out on the water - hopefully the afternoon will bring a different picture.
554. IKE
From this mornings San Juan discussion..."A second impressive looking tropical wave on satelitte near 30w
this morning...is forecast to reach the area by the middle of next
week. Latest model guidance brings this wave just north of Puerto
Rico and the U.S. Virgin Islands by late Wednesday/early Thursday
of next week...indicating a significant increase in weather with
this feature if current guidance pans out. Current forecast
increases shower and thunderstorm coverage Wednesday afternoon
through Thursday of next week to cover this feature."
AMO Vs Global Warming On Hurricane Activity
From since the start of 1995 upon until the present there has been increase hurricane activity in the Atlantic and rare formations as seen above for Cyclone Catarina. There are currently to theories to explain the increase activity. There is the theory of Global Warming and NOAAs explanation of the Atlantic Multidecadal Oscillation.

In your opinion, which is the more likely cause of increase hurricane activity. You can also give reasons why.

You leave your comments at my blog.
i think this is our next system....looks very healthyLink
almost feels like very early fall in Atlanta this morning.
558. IKE
From this mornings tropical weather discussion... African dust continues to move
off Africa covering the tropical Atlc from Africa to the E
Caribbean...suppressing convection and possible tropical
559. IKE
Atlanta has a dew point of 57!!!! IN JULY!
that discussion doesn't mean much to me anymore. Wilma STREGTHENED in 30kt shear before hitting here in SW FL...Alberto did the same this year.. i think that rule is starting to be discarded in some ways
weatherguru...Agree. Shear is no longer one of my most important factors in predicting storm development. Too many events in previous seasons has changed my thinking on the shear issue.
562. PBG00
75 dew pt here Ike and 94% humidity..trade ya!
I think once a storm has formed the shear sometimes doesn't matter..as with wilma and alberto.But it hinders the formation of a storm from infancy...Thats my take on it anyway
563. MZT
57F dewpoint here in Charlotte too. These late season Canadian highs are nice. Wish they'd happen more often.
564. MZT
That is a funky wave out there. It looks like a centipede. Hard for me to beleive every one of those cells will go poof. My gut says something outta come out of there.
Well, this morning does not seem to hold any new information in the BOC. Pressures are rising slightly.
Morning all. Welcome guru and iceman. Nothing too interesting out there right now. None of the models are showing development of anything in the next 100hrs, then out past that they don't seem to develop the same systems. So I would think it will be a slow week out there, although there is the outside chance that things can change unexpectedly, but not very likely. What I find most interesting is the old ULL that has been hanging out above PR.

Anywho, StormJunkie.com has all of the models, imagery, marine data, wind shear information, and much more that can help us understand the current state of the tropics.

junkie..r u a meteorologist..i have the same models as you do. but think something will develop..we all know how models can change at anytime. Times are changing
that wave looks real healthy.nice rotation and convection w/it. The weather channel made it a point this morning to talk about it
how the wave doing today thats we where all talking about last night
It is very nice out in sarasota i was suprised that the hi is 79
Pressures are high and the trades are averaging 20kts gusting to 30+ all over the Atlantic and Carib. Something drastic would have to occur for anything there.
hmmm they the mb falling with that wave
gulfport, fl - dew point 73, temp 78, humidity 84, pressure rising, winds ene at 5. if the clouds clear and burn this humidity we could see a nice day out of this...
However...that ULL above PR has had my interest since Wednesday and this morning it is now in the area where I start watching more closely.
575. MZT
Well that ULL is drifting slowly NNW. It's big, but gradually making room for that wave.

Guess I'll check back late tonight. It's too nice a day, to blog it all away.
576. MZT
Meant drifting WNW. Duh.
577. IKE
That ULL appears to be moving slightly north of west...suppose to haed for Florida's east coast.
I suppose we'll see how it behaves once over warmer waters around the Bahamas.
Stormy2day, Told you my forecasting was crude. Tomorrow might be a better boating day.
Ike, Dr Lyons stated that ULL was only going to effect the Turks and Caicos before heading N. Not sure what takes it N, but that is what he said about an hour agoa if I am not mistaken.

Geuss the trough will just absorb it and pull it north.

chef, I've not yet given up on today ...couple more mugs of coffee and a little more sun might make all the difference. If that doesn't pan out - the Yankees are in town. Either way, its a good day.
Go Devil Rays !!!!!
Does this ULL pressure system n/o PR have much chance to develop from a cold core syst to a tropical depression?
StormJunkie - I think you compiled a list of three ways an ULL goes extratropical. The P.R. low looks like case #4. It still looks like an upper level low around the edges, with dry air and upper-level cyclonic winds, but in the center there is a large area of moisture, low-topped convection and low wind shear. I can see if the convective cells get too far away from the center, they get sheared by the surrounding upper-level cyclonic winds.
So this system looks to be in an intermediate stage of tropical transition, not there yet (and may not ever get there), but trying to come down to the surface.

Maybe that fits one of your three cases already, I didn't go back and check; but if this did ever develop it would start off as a smaller ULH with a surface low underneath embedded in a larger dying ULL.
Thanks friends for that description. I did see that earlier discussion about UUL systems. I just was too lazy to find it. I will now focus on the central alantic system with good outflow and promise for develpmnt!
Melissa here...GORGEOUS day here in Savannah - very cool, breezy, doesn't feel at all humid. Wondering if I woke up somewhere different this morning cause it feels like fall. What is up with this stuff?
Strike extratropical from my above post...I meant to say tropical in the first sentence. Man I was up too late last night...

I don't think there is a big chance that this system goes fully tropical: there is some moisture at the center, but it is all surrounded by dry air. I just wanted to point out that it looks like an an old dying ULL that is coming down to the surface and is in an intemediate stage of transition.

OK, time to "take advantage of the morning" outside before any rain has a chance to get going. See everyone later.
That trough brought in some nice cool dry Canadian air with it Mel. Right up the rode from you and it is wonderfull here in Charleston also.

591. 900MB
If the ULL N of Puerto Rico does go tropical, I think it something we up in the NorthEast will have to keep an eye on. We are so overdue it's nuts.
See ya guygee. I think that kind of fits in with the ULL transitioning to the surface, although I agree that this has very little chance of developing, but it is the most interesting feature right now if you ask me

You know that you've been looking at too many Nexrad images when you walk into your backyard, look at the skies and try to scroll to the "hide clutter" option...

chef - I'm heading out in the boat while there is still a good ese wind and anything of significance falling south. The cloud cover should make for a cool day on the water. I'll catch the Rays/Yankees tomorrow night. (Rays always play their best games against the Yankees!)

Later all - have a great day - get out and enjoy!