A quiet day in the tropics

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

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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

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593. Stormy2day
2:53 PM GMT on July 08, 2006
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!


Member Since: June 29, 2006 Posts: 0 Comments: 306
592. StormJunkie
2:44 PM GMT on July 08, 2006
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

SJ
Member Since: August 17, 2005 Posts: 26 Comments: 15633
591. 900MB
2:36 PM GMT on July 08, 2006
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.
Member Since: June 11, 2006 Posts: 0 Comments: 660
590. StormJunkie
2:35 PM GMT on July 08, 2006
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.

SJ
Member Since: August 17, 2005 Posts: 26 Comments: 15633
589. guygee
2:33 PM GMT on July 08, 2006
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.
Member Since: September 16, 2005 Posts: 0 Comments: 3141
588. melwerle
2:31 PM GMT on July 08, 2006
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?
Member Since: June 28, 2006 Posts: 12 Comments: 1837
587. sails1
2:19 PM GMT on July 08, 2006
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!
Member Since: May 26, 2003 Posts: 0 Comments: 72
586. chefjeff
2:15 PM GMT on July 08, 2006
yes
585. guygee
2:14 PM GMT on July 08, 2006
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.
Member Since: September 16, 2005 Posts: 0 Comments: 3141
584. sails1
2:13 PM GMT on July 08, 2006
Does this ULL pressure system n/o PR have much chance to develop from a cold core syst to a tropical depression?
Member Since: May 26, 2003 Posts: 0 Comments: 72
583. chefjeff
1:57 PM GMT on July 08, 2006
Go Devil Rays !!!!!
582. Stormy2day
1:54 PM GMT on July 08, 2006
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.
Member Since: June 29, 2006 Posts: 0 Comments: 306
581. StormJunkie
1:52 PM GMT on July 08, 2006
Geuss the trough will just absorb it and pull it north.

SJ
Member Since: August 17, 2005 Posts: 26 Comments: 15633
580. StormJunkie
1:50 PM GMT on July 08, 2006
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.

SJ
Member Since: August 17, 2005 Posts: 26 Comments: 15633
579. chefjeff
1:50 PM GMT on July 08, 2006
Stormy2day, Told you my forecasting was crude. Tomorrow might be a better boating day.
578. Randrewl
1:42 PM GMT on July 08, 2006
I suppose we'll see how it behaves once over warmer waters around the Bahamas.
Member Since: June 8, 2006 Posts: 114 Comments: 31533
577. IKE
1:39 PM GMT on July 08, 2006
That ULL appears to be moving slightly north of west...suppose to haed for Florida's east coast.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
576. MZT
1:35 PM GMT on July 08, 2006
Meant drifting WNW. Duh.
Member Since: September 24, 2005 Posts: 0 Comments: 793
575. MZT
1:32 PM GMT on July 08, 2006
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.
Member Since: September 24, 2005 Posts: 0 Comments: 793
574. Randrewl
1:31 PM GMT on July 08, 2006
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.
Member Since: June 8, 2006 Posts: 114 Comments: 31533
573. Stormy2day
1:31 PM GMT on July 08, 2006
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...
Member Since: June 29, 2006 Posts: 0 Comments: 306
572. Tazmanian
1:28 PM GMT on July 08, 2006
hmmm they the mb falling with that wave
Member Since: May 21, 2006 Posts: 5091 Comments: 114696
571. Randrewl
1:25 PM GMT on July 08, 2006
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.
Member Since: June 8, 2006 Posts: 114 Comments: 31533
570. chessrascal
1:25 PM GMT on July 08, 2006
It is very nice out in sarasota i was suprised that the hi is 79
569. Tazmanian
1:24 PM GMT on July 08, 2006
how the wave doing today thats we where all talking about last night
Member Since: May 21, 2006 Posts: 5091 Comments: 114696
568. weatherguru
1:24 PM GMT on July 08, 2006
that wave looks real healthy.nice rotation and convection w/it. The weather channel made it a point this morning to talk about it
567. weatherguru
1:22 PM GMT on July 08, 2006
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
566. StormJunkie
1:16 PM GMT on July 08, 2006
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.

SJ
Member Since: August 17, 2005 Posts: 26 Comments: 15633
565. Randrewl
1:06 PM GMT on July 08, 2006
Well, this morning does not seem to hold any new information in the BOC. Pressures are rising slightly.
Member Since: June 8, 2006 Posts: 114 Comments: 31533
564. MZT
1:03 PM GMT on July 08, 2006
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.
Member Since: September 24, 2005 Posts: 0 Comments: 793
563. MZT
1:01 PM GMT on July 08, 2006
57F dewpoint here in Charlotte too. These late season Canadian highs are nice. Wish they'd happen more often.
Member Since: September 24, 2005 Posts: 0 Comments: 793
562. PBG00
12:53 PM GMT on July 08, 2006
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
Member Since: October 20, 2005 Posts: 14 Comments: 6650
561. Randrewl
12:52 PM GMT on July 08, 2006
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.
Member Since: June 8, 2006 Posts: 114 Comments: 31533
560. weatherguru
12:47 PM GMT on July 08, 2006
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
559. IKE
12:41 PM GMT on July 08, 2006
Atlanta has a dew point of 57!!!! IN JULY!
Member Since: June 9, 2005 Posts: 23 Comments: 37858
558. IKE
12:40 PM GMT on July 08, 2006
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
formation.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
557. ICEMAN
12:37 PM GMT on July 08, 2006
almost feels like very early fall in Atlanta this morning.
556. weatherguru
12:33 PM GMT on July 08, 2006
i think this is our next system....looks very healthyLink
555. Cavin Rawlins
12:29 PM GMT on July 08, 2006
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 NOAA’s 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.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
554. IKE
12:17 PM GMT on July 08, 2006
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."
Member Since: June 9, 2005 Posts: 23 Comments: 37858
553. Stormy2day
12:07 PM GMT on July 08, 2006
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.
Member Since: June 29, 2006 Posts: 0 Comments: 306
552. PBG00
12:01 PM GMT on July 08, 2006
Mornin all...Waking up to more rain..in for some severe storms this afternoon..thanks to our front.
Member Since: October 20, 2005 Posts: 14 Comments: 6650
551. Randrewl
11:55 AM GMT on July 08, 2006
I can't remember the last time I saw a cold front dip this far south in July! Very strange.
Member Since: June 8, 2006 Posts: 114 Comments: 31533
550. chefjeff
11:54 AM GMT on July 08, 2006
N. of Puerto rico is gathering moisture along with the circulation, Keep an eye on it.
549. pcolabob
11:35 AM GMT on July 08, 2006
Ike

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.
Member Since: August 3, 2011 Posts: 0 Comments: 0
548. EdMahmoudHome
11:20 AM GMT on July 08, 2006
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.
547. chefjeff
11:18 AM GMT on July 08, 2006
If it don't stop rainin' here in Fort Myers this weekend I'll need a bush hog to mow my yard.
546. EdMahmoudHome
11:16 AM GMT on July 08, 2006
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.
545. chefjeff
11:13 AM GMT on July 08, 2006
Did Belize get relocated ? It can't possibly cross that terrain!
544. EdMahmoudHome
11:12 AM GMT on July 08, 2006
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'
543. EdMahmoudHome
11:06 AM GMT on July 08, 2006
In my un-expert opinion, the Belize Blob will become a tropical cyclone.



In the Pacific.

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.