Rare South Atlantic subtropical cyclone forms; severe weather season in U.S. underway

By: Dr. Jeff Masters , 2:10 PM GMT on March 10, 2010

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A rare weather event is underway in the South Atlantic Ocean, where the basin's 7th recorded tropical or subtropical cyclone of all-time has formed. An area of disturbed weather (Invest 90Q) off the coast of Brazil, near 30S 48W, attained a well-defined surface circulation, top wind speeds of tropical depression strength (35 mph), a warm core in the bottom portion of the atmosphere, and a cold core aloft last night. If this storm had been in the North Atlantic, there is a good chance it would have been named Subtropical Depression One. However, tropical and subtropical storms are so rare in the South Atlantic that there is no official naming of depressions or storms done. The cyclone had top winds of at least 35 mph as seen on an ASCAT pass at 7:02 am EST this morning (Figure 2), and satellite estimates of the storm's intensity topped out at 40 mph (minimum subtropical storms strength) last night. This morning, the satellite estimates are showing that the system has weakened to a 35 mph tropical depression. There is some moderate wind shear interfering with development, and sea surface temperatures are about 25°C, which is about 1°C below what is typically needed to support a tropical storm. The storm is headed eastward out to sea, and is not a threat to any land areas. The models show the storm will lose its tropical characteristics and get absorbed by a frontal system by Saturday.


Figure 1. Afternoon visible satellite image of the Brazilian Invest 90Q.


Figure 2. Satellite-measured winds from ASCAT clearly show the circulation of the cyclone in this pass from 7:02 am EST on March 10, 2010. Top winds as seen be ASCAT were 30 knots (35 mph), just below the 40 mph needed for it to be a tropical storm. Image credit: NOAA/NESDIS/ORA.

Brazil has had only one landfalling tropical cyclone in its history, Cyclone Catarina of March 2004. Catarina is one of only six known tropical or subtropical cyclones to form in the South Atlantic, and the only one to reach hurricane strength. Tropical cyclones rarely form in the South Atlantic Ocean, due to strong upper-level wind shear, cool water temperatures, and the lack of an initial disturbance to get things spinning (no African waves or Intertropical Convergence Zone exist in the proper locations in the South Atlantic to help spawn tropical storms). Today's storm is located close to where Catarina formed.

Severe weather season begins
It's March, and that means severe weather season will get underway in earnest for the Midwest U.S., and powerful spring storm systems draw warm, moist air from the Gulf of Mexico northward, to collide with cold, dry air from Canada. It's been a quiet early season, with only 42 tornadoes reported thus far this year (as of Sunday), compared to a normal 70 - 100 twisters. There was only one tornado in the U.S. in February, in a San Joaquin Valley oilfield in California two weekends ago. A year ago, there were 36 February tornadoes, and the year's deadliest tornado occurred on Feb. 10, 2009, in Lone Grove, Oklahoma, where eight people died in a storm with winds estimated at 170 mph. But thanks to a very wet winter and a continued active jet stream pattern that will pull strong storms through the Midwestern U.S. this month, expect at least an average March for severe weather. NOAA's Storm Prediction Center is forecasting a "slight" chance of severe weather across a large portion of the Mississippi Valley today, in association with a strong cold front that will be plowing through the region. Strong thuderstorms capable of generating damaging winds and large hail should develop along the front from southeast Kansas through eastern Oklahoma into NE Texas by middle/late afternoon. The storms should consolidate into broken bands and move into Missouri and and Arkansas by early evening. Isolated tornadoes are also possible in the entire "slight" risk area.


Figure 3. Severe weather forecast for today from the NOAA Storm Prediction Center.

Hurricane Hugo talk
I'm presenting a talk to a class at the University of Michigan this morning on my 1989 flight through Hurricane Hugo. You can listen in live starting at about 10:10 - 10:15 am EST by pointing your browser to http://samson.lecturetools.org/. You'll need to have Apple Quicktime installed. If all goes well, the talk will be recorded and you can view it later, as well.

Jeff Masters

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Holy cow, I haven't even heard about this quake...happened after the passage of the giant Mediterranean storm. Link
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Quoting Skyepony:
Click this & animate the last 8 frames.. the low in the central part of US sucks in the severe low out of the SW to dance as it establishes a good tap to the ITCZ down deep in the Pacific.


Hmm, a frontal storm exploding within the centre of another frontal storm while the first one expands and weakens. We've seen this occurring at least once earlier this winter.
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What does the difference between the two maps represent,and how does it affect this years hurricane season?
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Quoting Jeff9641:


I was wondering where you guys go this map from. TKS!

*Most* of the plots I post usually come from somewhere in the links in my blog: http://www.wunderground.com/blog/atmoaggie/comment.html?entrynum=2

Mostly tropical. CONUS severe near the bottom.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
346. JRRP
2006 High 1034

2010 High 1022

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Quoting StormW:


Who the "hail" knows. LOL!

Oh, that's good.
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Quoting atmoaggie:

Things my dog would gladly eat.

WRONG answer.
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Quoting Chicklit:
GOLFBALL TO HEN EGG SIZE HAIL REPORTED.
ahhh...you're right.
I suppose that is to clarify they weren't robin-sized eggs.

Or ostrich...ouch.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting Jeff9641:
Dr Greg Forbes says this will go all night and we could have some F3 tornadoes in the mix so people in south have your NOAA weather radio on. Diffluent air over the southern states right now with dewpoints in the 60's. Jet max of 195 knts in the area as well.

Nice plot of the temps and dewpoints current as of 30 minutes ago here: http://twister.sbs.ohio-state.edu/surface/sp.gif
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting Chicklit:
What do pennies, nickels, walnuts, golf balls, eggs and hens have in common?

Things my dog would gladly eat.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
GOLFBALL TO HEN EGG SIZE HAIL REPORTED.
ahhh...you're right.
I suppose that is to clarify it wasn't robin-sized egg hail. Sheesh. I particularly liked the hen visual due to my moniker.
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Riddle:
What do pennies, nickels, walnuts, golf balls, and hen eggs have in common?
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Quoting Chicklit:
Hi Atmo,
Now why would they say "hen egg?"
And egg is an egg and we all know where they come from. I think it was hen-sized hail.

I dunno, I don't make it up. Look at post 297.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Hi Atmo,
Now why would they say "hen egg?"
And egg is an egg and we all know where they come from. I think it was hen-sized hail.
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Quoting Chicklit:
Evening Wunderfolk.
I heard it was hailing baseballs and hens somewhere tonight. Was that Bama?
Good grief!

I think that was hen-egg sized hail in southern Arkansas...they should know what size that is there!
Member Since: August 16, 2007 Posts: 6 Comments: 12463
I have been wondering all day what Pottery is doing for water now that a snake has contaminated his 300 gallon cistern.
Understand they're in borderline drought conditions in the Antilles after a weak tropical season last year and the typically dry winter months.
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Evening Wunderfolk.
I heard it was hailing baseballs and hens somewhere tonight. Was that Bama?
Good grief!
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Looking at the soundings from 0 Z...looks like more of the same for Arkansas...hail.

Down here, the Slidell WFO launch actually shows some match to nado possibilities. Looks like our reprieve is over (one reported nado near the coast in S Central LA, already.)

NOLA / BR sounding (Slidell):

Click for full size


All soundings here: http://w1.spc.woc.noaa.gov/exper/soundings/
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting nrtiwlnvragn:
314. atmoaggie

Was sad to hear about Joanne Simpson.

Yeah. Lost a pioneer in hurricane dynamics, among other things.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
319. HadesGodWyvern (Mod)
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314. atmoaggie

Was sad to hear about Joanne Simpson.
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317. HadesGodWyvern (Mod)
Seychelles Meteorological Services
Tropical Disturbance Advisory Number EIGHT
DEPRESSION SUR TERRE. FORMER HUBERT (13-20092010)
4:00 AM Réunion March 11 2010
====================================

At 0:00 AM UTC, Overland Depression, Former Hubert (990 hPa) located at 21.0S 48.2E has 10 minute sustained winds of 50 knots with gusts of 70 knots. The storm is reported as moving west at 4 knots.

Dvorak Intensity:

Storm Force Winds
=================
within the center

Gale-Force Winds
=================
40 NM from the center

Near Gale-Force Winds
=====================
40 NM from the center

Forecast and Intensity
=====================
12 HRS: 21.3S 46.6E - (Depression sur terre)
24 HRS: 21.9S 45.1E - (Se Dissipant)

Additional Information
=======================
According to satellite imagery (METEO SAT7, NOAA 18 and 19 of 2151z and 2238z), Hubert has made landfall near Mananjary as a severe tropical storm after resumed a westward track over the last hours.

System should maintain a general west southwest track on the northwestern edge of the subtropical highs. Therefore, it is expected to remain overland over the next 24 hours and should dissipate. On late Friday, available 1200z Numerical Weather Prediction models make a remnant low move back over water off the Malagasy southwestern coast (Tulear area). If this happens, potential for re-intensification appears to be poor due to increasing northwesterly shear.
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316. HadesGodWyvern (Mod)
SPECIAL STATEMENT. AS DETERMINED BY NOAA NESDIS...THE CYCLONE OFF
THE SOUTHERN COAST OF BRASIL IS NOW A TROPICAL DEPRESSION.
THE
CYCLONE CENTERS NEAR 30S 48W. WINDS ARE ESTIMATED AT 25KT IN
CLOSED VICINITY TO THIS CYCLONE. THE UPPER LEVEL TROUGH...WHICH
PREVIOUSLY SUSTAINED SUBTROPICAL CHARACTERISTICS...IS RAPIDLY
DECOUPLING FROM THIS SYSTEM AS ANOTHER TROUGH MOVES ACROSS MID
SECTIONS OF SOUTH AMERICA. IN A LULL BETWEEN
PERTURBATIONS...THERE IS A GOOD POSSIBILITY THAT THE SHEAR ALOFT
MIGHT WEAKEN ENOUGH TO ALLOW SOME INTENSIFICATION OF THIS SYSTEM
DURING THE EVENING HOURS. SO CANNOT RULE OUT POSSIBILITY OF THIS
SYSTEM STRENGTHENING TO A TROPICAL STORM AS IT TAKES ADVANTAGE OF
FAVORABLE SEA SURFACE TEMPERATURES. BUT AS THE STEERING FLOW IS
TO REMAIN FROM THE WEST...THIS SYSTEM IS VERY LIKELY TO MEANDER
OFFSHORE DURING THE NEXT 30-36 HRS...THEN WEAKEN TO A REMNANT LOW
THROUGH 48 HRS. THE TIGHT/COMPACT CYCLONE IS LIKELY TO FAVOR
ISOLATED TO SCATTERED CONVECTION ON THE SERRA DO MAR...WITH
ACCUMULATION OF 15-25MM/DAY THROUGH 24-30 HRS. MOST INTENSE
ACTIVITY IS EXPECTED OFFSHORE AND IN CLOSE VICINITY TO THE
CYCLONE.
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315. HadesGodWyvern (Mod)
Fiji Meteorological Services
Tropical Disturbance Advisory #2
TROPICAL DEPRESSION 14F
12:00 PM FST March 11 2010
======================================

A TROPICAL CYCLONE ALERT IS NOW IN FORCE FOR WALLIS AND FUTUNA.

A STRONG WIND WARNING IS NOW IN FORCE FOR WALLIS AND FUTUNA.


At 0:00 AM UTC, Tropical Depression 14 (1002 hPa) located at 11.2S 174.3W has 10 minute sustained winds of 20 knots. Position POOR based on hourly GMS/GOES enhanced infrared and visible imagery with animation. The depression is reported as moving southwest at 10 knots.

Organization has improved past 24 hours. The system lies over a weakly sheared and diffluent environment. Sea surface temperature is around 30C. System steered west southwest by northeast deep layer mean flow.

Dvorak analysis based on 0.35 wrap on LOG10 spiral yielding DT 2.0

Dvorak Intensity: T2.0/2.0/D1.0/24HRS

Global models agree on west southwest track and intesification.

Forecast and Intensity
========================
12 HRS: 11.3S 175.3W - 25 knots (Tropical Depression)
24 HRS: 11.8S 176.6W - 30 knots (Tropical Depression)
48 HRS: 13.6S 179.1W - 50 knots (CAT 2)

The Next Tropical Disturbance Advisory On TD 14F Will Be Issued At Around 08:30 AM UTC...
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Quoting nrtiwlnvragn:
307. atmoaggie

There was a good presentation on COAMPS-TC at this years interdepartmental hurricane conference.

Yep, thanks, saw that one.

Rich Hodur and Sue Chen, good people. (Seriously, the met world is one not-so-big family. Everyone knows everyone.)

Y'all know that Sue Chen has been the Fortran coder behind a lot of our models? MM5, COAMPS, WRF, GFDL(?). That Lady has done more for our numerical modeling than any other...except maybe Eugena Kalnay and Joanne Simpson.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Perturbation theory, mathematical methods that give approximate solutions to problems that cannot be solved exactly

Perturbation (geology), changes in the nature of alluvial deposits over time

Perturbation (astronomy), alterations to an object's orbit e.g. caused by gravitational interactions with other bodies

Perturbation theory (quantum mechanics), a set of approximation schemes directly related to mathematical perturbation for describing a complicated quantum system in terms of a simpler one

Perturbation (biology), an alteration of the function of a biological system, induced by external or internal mechanisms

Perturbation (economic), an alteration of the function of an economic system, induced by external or internal mechanisms

Perturbation (machine learning), making changes in the dataset to (re)learn a classifier (used in bagging and boosting).
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307. atmoaggie

There was a good presentation on COAMPS-TC at this years interdepartmental hurricane conference.
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"Perturbations"

Now there is a word you don't often get a chance to use in a sentence! LOL
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SPECIAL STATEMENT. AS DETERMINED BY NOAA NESDIS...THE CYCLONE OFF
THE SOUTHERN COAST OF BRASIL SEEMS TO BE TAKING TROPICAL
CHARACTERISTICS. FINAL DESIGNATION...HOWEVER...IS AT THE
JUDGEMENT OF BRAZILIAN AUTHORITIES. PER THE IMAGERY...THE CLOSED
LOW CENTERS NEAR 30S 48W. WINDS ARE ESTIMATED AT 35KT IN CLOSED
VICINITY TO THIS CIRCULATION. THE UPPER LEVEL TROUGH...WHICH
PREVIOUSLY SUSTAINED SUBTROPICAL CHARACTERISTICS...IS RAPIDLY
DECOUPLING FROM THIS SYSTEM AS ANOTHER TROUGH MOVES ACROSS MID
SECTIONS OF SOUTH AMERICA. IN A LULL BETWEEN PERTURBATIONS...
THERE IS A GOOD POSSIBILITY THAT THE SHEAR ALOFT MIGHT WEAKEN
ENOUGH TO ALLOW SOME INTENSIFICATION OF THIS SYSTEM DURING THE
EVENING HOURS. SO CANNOT RULE OUT POSSIBILITY OF THIS SYSTEM
STRENGTHENING AS IT TAKES ADVANTAGE OF FAVORABLE SEA SURFACE
TEMPERATURES. BUT AS THE STEERING FLOW IS TO REMAIN FROM THE
WEST...THIS SYSTEM IS TO MOVE EAST-SOUTHEAST DURING THE NEXT
36 HRS...THEN WEAKEN TO A REMNANT LOW THROUGH 48 HRS.
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Quoting Skyepony:
Click this & animate the last 8 frames.. the low in the central part of US sucks in the severe low out of the SW to dance as it establishes a good tap to the ITCZ down deep in the Pacific.


Looks kind of like a fujiwhara effect.
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Quoting Grothar:


Are you serious? I thought you were kidding when you said you were going to do that.

??? Completely serious. We've been running COAMPS operationally for about 8 years in my shop.
Quoting Grothar:


\They whole thing is making less sense. There are some links I might send you this week on question and answer blog on the different systems.

Well, let me see what happens. Boss has been friends with Bill Burnett, NDBC chief, almost as long as we've been running COAMPS. I think they go to church together, too. Hit him up for some info today.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting xcool:
i buy g


That g better stand for a generator if this season keeps up. Looks like an active season ahead. Better keep those graphics coming, xcool.
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Ugly!

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304. Skyepony (Mod)
Click this & animate the last 8 frames.. the low in the central part of US sucks in the severe low out of the SW to dance as it establishes a good tap to the ITCZ down deep in the Pacific.
Member Since: Posts: Comments:

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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.

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