Hurricane season begins today; normal June activity expected

By: Dr. Jeff Masters , 1:38 PM GMT on June 01, 2009

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Hurricane season is upon us, and it's time to take a look at the prevailing conditions and 2-week forecast for tropical cyclone activity in the Atlantic. June is typically the quietest month of the Atlantic hurricane season. On average, we see only one named storm every two years in June. Only one major hurricane has made landfall in June--Category 4 Hurricane Audrey of 1957, which struck the Texas/Louisiana border area on June 27 of that year, killing 550. The highest number of named storms for the month is three, which occurred in 1936 and 1968. In the fourteen years since the current active hurricane period began in 1995, there have been eleven June named storms (if we include last year's Tropical Storm Arthur, which really formed on May 31). Five tropical storms have formed in the first half of June in that 14-year period, giving a historical 36% chance of a first-half-of-June named storm.


Figure 1. Tracks of all June tropical storms and hurricanes, 1851 - 2007.

Sea Surface Temperatures
Sea Surface Temperatures (SSTs) are close to average over the tropical Atlantic between Africa and Central America this year (Figure 2). These temperatures are some of the coolest we've seen since 1995, when the current active hurricane period began. This year's cool SSTs should prevent a repeat of the unforgettable Hurricane Season of 2005, which had the highest SSTs on record in the tropical Atlantic. Note also that SSTs along the Equatorial Pacific off the coast of South America are quite a bit above average, signaling the possible start of an El Niño episode. As I discussed in Friday's post, odds are increasing for a weak El Niño to form in time for hurricane season, and this should cut down on the number and intensity of Atlantic tropical storms and hurricanes this year. However, if an El Niño is developing, it shouldn't start affecting Atlantic hurricane activity until August.

Typically, June storms only form over the Gulf of Mexico, Western Caribbean, and Gulf Stream waters just offshore Florida, where water temperatures are warmest. SSTs are 26 - 28°C in these regions, which is about 0.5°C above average for this time of year. June storms typically form when a cold front moves off the U.S. coast and stalls out, with the old frontal boundary serving as a focal point for development of a tropical disturbance. African tropical waves, which serve as the instigators of about 85% of all major hurricanes, are usually too far south in June to trigger tropical storm formation. Every so often, a tropical wave coming off the coast of Africa moves far enough north to act as a seed for a June tropical storm. This was the case for Arthur of 2008 (which also had major help from the spinning remnants of the Eastern Pacific's Tropical Storm Alma). Another way to get Atlantic June storms is for a disturbed weather area in the Eastern Pacific Intertropical Convergence Zone (ITCZ) to push north into the Western Caribbean and spawn a storm there. This was the case for Tropical Storm Alberto of 2006 (which may have also had help from an African wave). SSTs are too cold in June to allow storms to develop between the coast of Africa and the Lesser Antilles Islands--there has only been once such development in the historical record--Ana of 1979, which coincidentally will be the name given to this year's first storm.


Figure 2. Sea Surface Temperature (SST) departure from average for June 1, 2009. SSTs were near average over the tropical Atlantic. Note the large region of above average SSTs along the Equatorial Pacific off the coast of South America, signaling the possible start of an El Niño episode. Image credit: NOAA/NESDIS.

Tropical Cyclone Heat Potential
It's not just the SSTs that are important for hurricanes, it's also the total amount of heat in the ocean to a depth of about 150 meters. Hurricanes stir up water from down deep due to their high winds, so a shallow layer of warm water isn't as beneficial to a hurricane as a deep one. The Tropical Cyclone Heat Potential (TCHP, Figure 3) is a measure of this total heat content. A high TCHP over 80 is very beneficial to rapid intensification. As we can see, the heat energy available in the tropical Atlantic has declined considerably since 2005, when the highest SSTs ever measured in the tropical Atlantic occurred. TCHP this year is similar to last year's levels, which were high enough to support five major hurricanes.


Figure 3. Tropical Cyclone Heat Potential (TCHP) for May 31 2005 (top), May 31 of last year (middle) and May 30 2009 (bottom). TCHP is a measure of the total heat energy available in the ocean. Record high values of TCHP were observed in 2005. TCHP this year is much lower, and similar to last year. Image credit: NOAA/AOML.

Wind shear
Wind shear is usually defined as the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude). In most circumstances, wind shear above 20 knots will act to inhibit tropical storm formation. Wind shear below 12 knots is very conducive for tropical storm formation. High wind shear acts to tear a storm apart. The jet stream's band of strong high-altitude winds is the main source of wind shear in June over the Atlantic hurricane breeding grounds, since the jet is very active and located quite far south this time of year.

The jet stream over the past few weeks has been locked into a pattern where a southern branch (the subtropical jet stream) brings high wind shear over the Caribbean, and a northern branch (the polar jet stream) brings high wind shear offshore of New England. This leaves a "hole" of low shear between the two branches off the coast of North Carolina, which is where Tropical Depression One formed. The low shear "hole" has dipped down into the northern Gulf of Mexico a few times. Disturbance 90L, which almost developed into a tropical storm before it came ashore in Mississippi/Alabama on May 23, took advantage of one of these low-shear areas.

The jet stream is forecast to maintain this two-branch pattern over the coming ten days. This means that the waters offshore of the Carolinas are the most likely place for a tropical storm to form during this period, though the northern Gulf of Mexico will at times have shear low enough to allow tropical storm formation. The latest 16-day forecast by the GFS model (Figure 4) predicts that the subtropical jet will weaken and retreat northwards by the middle of June, creating low-shear conditions over the Caribbean. This is a typical occurrence for mid-June, and we need to start watching the Western Caribbean for tropical storm formation by the middle of the month.


Figure 4. Wind shear forecast from the 00Z GMT June 1, 2009 run of the GFS model for June 1 (left panel) and June 17 (right panel). Currently, the polar jet stream is bringing high wind shear to the waters offshore New England, and the subtropical jet is bringing high wind shear to the Caribbean. This leaves the waters off the coast of North Carolina under low shear, making this area the most favored region for tropical storm formation over the next 7 - 10 days. By June 17, the subtropical jet is expected to weaken and move northwards, leaving the Caribbean under low shear, and favoring that region for tropical storm formation. Wind speeds are given in m/s; multiply by two to get a rough conversion to knots. Thus, the red regions of low shear range from 0 - 16 knots.

Dry air and African dust
It's too early to concern ourselves with dry air and dust coming off the coast of Africa, since these dust outbreaks don't make it all the way to the June tropical cyclone breeding grounds in the Western Caribbean and the Gulf of Mexico. Developing storms do have to contend with dry air from Canada moving off the U.S. coast; this was a key reason why 2007's Subtropical Storm Andrea never became a tropical storm. Dr. Amato Evan of the University of Wisconsin will issue his dust forecast for the coming hurricane season later this week, and I'll be discussing his forecast in an upcoming post.

Steering currents
The steering current pattern over the past few weeks has been typical for June, with an active jet stream bringing many troughs of low pressure off the East Coast of the U.S. These troughs are frequent enough and strong enough to recurve any tropical storms or hurricanes that might penetrate north of the Caribbean Sea. Steering current patterns are predictable only about 3-5 days in the future, although we can make very general forecasts about the pattern as much as two weeks in advance. At present, it appears that the coming two weeks will maintain the typical June pattern, bringing many troughs of low pressure off the East Coast capable of recurving any June storms that might form. There is no telling what might happen during the peak months of August, September, and October--we might be in for a repeat of the favorable 2006 steering current pattern that recurved every storm out to sea--or the unfavorable 2008 pattern, that steered Ike and Gustav into the Gulf of Mexico.

Summary
Recent history suggests a 36% chance of a named storm occurring in the first half of June. The current conditions in the atmosphere and ocean are near average, so expect about a 1/3 chance of a named storm between now and June 15. The computer models are currently not forecasting development of any tropical storms over the next seven days.

I'll have an update Tuesday afternoon, when I'll discuss the Colorado State University June Atlantic Hurricane season forecast by Dr. Phil Klotzbach and Dr. Bill Gray, which will be issued Tuesday morning.

My next analysis and 2-week outlook for hurricane season is scheduled for June 13.

Jeff Masters

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Quoting StormW:


You're welcome...yeah, I'm waitin' for them to start designating the polar vortex as an INVEST.


Maybe they'll post a storm warning for Mount Washington while they're at it... :-)
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743. IKE
Quoting StormW:


You're welcome...yeah, I'm waitin' for them to start designating the polar vortex as an INVEST.


LOL.

I get a kick out of how they describe 92L...."A NON-TROPICAL AREA OF LOW PRESSURE"

"non-tropical"? Then why are they even mentioning it?
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Lets all not forget our tinfoil hats.

Honestly though... the NHC is tasked with weather forecasting to protect the public. If they start naming every naked swirl or thunderstorm complex that could possibly develop maybe, the public would grow very tired of it, and stop heeding the warnings. IMO, STS should never be named, especially since they do not have a tropical structure, and their impacts are totally different than a tropical system's. (they are more rain than wind... and you can get just as much rain out of a baroclinic low)
Member Since: August 3, 2008 Posts: 16 Comments: 5869
Well, like in 2006, they will have to admit their mistakes when the re-analyze after the season is done.
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739. IKE
Buoy reading at 5:50 am CDST...buoy in the BOC....the reading is over 2 hours old, but it's the last one posted...

Wind Direction (WDIR): ESE ( 110 deg true )
5-day plot - Wind Speed Wind Speed (WSPD): 11.7 kts
5-day plot - Wind Gust Wind Gust (GST): 13.6 kts
5-day plot - Wave Height Wave Height (WVHT): 2.6 ft
5-day plot - Dominant Wave Period Dominant Wave Period (DPD): 4 sec
5-day plot - Average Period Average Period (APD): 3.6 sec
5-day plot - Atmospheric Pressure Atmospheric Pressure (PRES): 29.86 in
5-day plot - Pressure Tendency Pressure Tendency (PTDY): -0.04 in ( Falling )
5-day plot - Air Temperature Air Temperature (ATMP): 80.8 °F
5-day plot - Water Temperature Water Temperature (WTMP): 81.3 °F
5-day plot - Dew Point Dew Point (DEWP): 76.8 °F
5-day plot - Heat Index Heat Index (HEAT): 87.4 °F
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They just don't want to be proved wrong, so they don't name these storms, it's not wishcasting, look at 90L, tell me that wasn't at least Subtropical when it made landfall. They're on to a bad start this year, hopefully they will get better.
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NHC does have some of the best experts in the world on this issue (including, formerly, our Dr. Masters)and they do a great job and have been steadily improving forecasting issues over the past 15 years....However, all experts recognize that the biggest gap is in the realm of intensifcation issues; that 90L just deepend quite a bit just as it made landfall when it hit the pocket of favorable shear..Don't blame NHC for that one..
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Isn't the shear forcast to become more favorable in the vicinity of GOM blob?
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Quoting IMA:
Homeless, tell me about it. Too dang hot & sticky, & it started too early! Just praying for more rain - for the aquifer AND so I can stand out in it to cool off. lol


Lol. We're back to the usual 20-30% chance every evening. Sigh getting too hot to fish too. Lol.
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Quoting jeffs713:


Thank you, StormW, for the humor in the early AM.


Hilarious.
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Quoting StormW:


Good morning, Ma'am!


Seems like this is almost the opposite of last year, when a system almost had to be ready to name before they looked at it?
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722: Better experts at the NHC? Where do you expect to find better experts than the National Hurricane Center? Maybe if we stop wishcasting every storm into an apocolypto-cane...

Really. Its getting old. The NHC upgrades objectively, based on very standard criteria. The latest thing up by the Azores did not have the winds for an upgrade. 90L didn't have the organization and sustained winds until very late.
Member Since: August 3, 2008 Posts: 16 Comments: 5869
Quoting cg2916:
Nothing much yet.


Convection is starting to wane already and sheer is starting to take it's toll on it as it nears that band of 50 MPH sheer just to it's north........We will probably have the answer (dissipation) by later today IMHO
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Critical?? There's a reason why I am critical. I have a friend who lives in the Panhandle of Florida.. He was actually heading to Mobile the day the Unnamed Tropical Storm (90L) made landfall. He said it was exactly like a 50 mph. Tropical Storm. Now TD1 never reached 40 mph, they were good on that.. but this is getting ridiculous with 92L. It's already a Subtropical Storm with 50 mph. Doesn't matter if it's in cooler waters, things happen, remember Vince anyone? NOTHING is impossible but the NHC doesn't want to be proved wrong like last year so they won't name many storms this year.
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Quoting StormW:


I think the NHC is bored...already lookin at stuff outside the tropics...I mean, NE of the Azores...gimme a break.


Thank you, StormW, for the humor in the early AM.
Member Since: August 3, 2008 Posts: 16 Comments: 5869
This is why the NHC isn't naming these things: their forecast was low for activity, so they're keeping the naming conservative.
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Quoting panamasteve:
Might want to start keeping an eye on that blob moving NE in the GOM...
Nothing much yet.
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I'm not sure why everyone is critical of the NHC. They have standards for naming these systems and apparently none of them have deserved to be named.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
I've already said this, but that is way too far north for June development. Even if it were September 10, I wouldn't count on formation.

P.S. Is this ST3.0 to you?
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Quoting homelesswanderer:


That is warmer! Didn't take long for the gulf to start cooking.

And Good Morning Storm.


Agreed. It's actually been warmer over the last few days. When I was looking back at the archive water temp data for both Fort Myers and Naples over the last couple days, they showed that Naples was actually up to 89 and Fort Myers was up to almost 87 yesterday afternoon. Not encouraging when the Gulf is like bathwater this early!
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Might want to start keeping an eye on that blob moving NE in the GOM...
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Actually if we had better experts at the NHC, this would be Subtropical Storm Bill and the one that hit Alabama should have been Tropical Storm Ana... This is getting ridiculous now, 92L needs to be upgraded. Stop the nonsense NHC!
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721. IMA
Homeless, tell me about it. Too dang hot & sticky, & it started too early! Just praying for more rain - for the aquifer AND so I can stand out in it to cool off. lol
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Quoting StormW:


I think the NHC is bored...already lookin at stuff outside the tropics...I mean, NE of the Azores...gimme a break.


LOL.
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Quoting StormW:


I think the NHC is bored...already lookin at stuff outside the tropics...I mean, NE of the Azores...gimme a break.

Haven't been a big fan of the NHC so far this year. 90L was tropical and the NHC knows it, they just didn't want to be wrong. TD1 should have been 40 mph. 92L shouldn't even be 92L.
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Quoting Cazatormentas:
The Tropica Storm Position Page is callig 92L as subtropical:

DATE/TIME LAT LON CLASSIFICATION STORM
02/1200 UTC 42.7N 23.8W ST3.0 92L
02/0600 UTC 41.7N 23.8W ST2.5 92L
01/2345 UTC 40.7N 23.9W ST2.5 INVEST
01/1745 UTC 39.9N 24.7W ST1.5 INVEST

ST: subtropical.

ST3.0? What's wrong with their satellite? It's not ST and how the heck is that 3.0?
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Quoting eye2theskies:


Not quite as warm to start here in Fort Myers, but the Gulf is warmer; 76 with a water temp of 84-86 between here and Naples


That is warmer! Didn't take long for the gulf to start cooking.

And Good Morning Storm.
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Since yesterday, 92L has been looking more tropical, but has become more extratropical. Yesterday it was all subtropical.
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The Tropica Storm Position Page is callig 92L as subtropical:

DATE/TIME LAT LON CLASSIFICATION STORM
02/1200 UTC 42.7N 23.8W ST3.0 92L
02/0600 UTC 41.7N 23.8W ST2.5 92L
01/2345 UTC 40.7N 23.9W ST2.5 INVEST
01/1745 UTC 39.9N 24.7W ST1.5 INVEST

ST: subtropical.

Moreover: 3.0 --> 45 KT winds...

Looking at those data, 92L could be classified as subtropical storm ANA, if I am right....
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Quoting StormW:
Good morning!

Hey, StormW. What's your take on 92L, I don't think it'll form anything.
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Quoting homelesswanderer:
Air Temperature (ATMP): 79.9 °F
Water Temperature (WTMP): 82.4 °F

Good morning.

Hot and sticky here in SE TX.
Gee we usually don't sart our
80 by 8 and 90 by 9 til at least july. lol


Not quite as warm to start here in Fort Myers, but the Gulf is warmer; 76 with a water temp of 84-86 between here and Naples
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Snippet from NWS Tallahassee discussion:

Tonight through Thursday...all models are generally indicating
decreasing upper heights along with increasing deep layer moisture
pushing north across the Gulf Coast from the central Gulf. Will
continue to indicate increasing rain chances through this period with
the best probabilities on Thursday as the front approaches from the
northwest. The GFS remains the more aggressive solution and develops
a surface low associated with a strong vorticity maximum south of New Orleans
later tonight...then shows it on a northeast track toward the
Panhandle coast through the day Wednesday with a quantitative precipitation forecast bomb of 5-10
inches and 20-30 knot winds across the waters. This is likely the
result of the typical feedback issues with this model due to the
fact that its convective precipitation values are only ranging from a
half of an inch to an inch and the GFS stable precipitation are the
higher values previously mentioned. Although this is an issue...an
mesoscale convective system like feature developing somewhere in the vicinity of the
central Gulf Coast through this time can't be ruled out...since
the GFS is more than likely properly sensing the appropriate
instability. To mitigate the high qpf/winds/seas...we will go with
a blend of the met/mav/locally ran probabilities to output more
realistic values.
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Okay - doesn't 92l look like it has an eye? LOL.
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Air Temperature (ATMP): 79.9 °F
Water Temperature (WTMP): 82.4 °F

Good morning.

Hot and sticky here in SE TX.
Gee we usually don't sart our
80 by 8 and 90 by 9 til at least july. lol
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Quoting CaneWarning:


You're right. I wonder if Dr. Masters will mention it in his update today. I don't think we have model consensus yet though.


Dr. Master's mentioned that little "pocket" of reduced shear in the very Northern part of the GOM near LA/AL/FL; much like the last low finally starting to get it's act together at the last minute before landfall last week...That's what I see in the model run Ike posted, but, the shear may rip this little area of convection apart before it ever gets to the promised land in the Upper GOM..
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Quoting IKE:
Maybe 93L comes out of the GOM....6Z NAM


You're right. I wonder if Dr. Masters will mention it in his update today. I don't think we have model consensus yet though.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Good Morning Folks....Very hot in the Florida Big Bend yesterday (high of 94) and plenty of moisture all around the Gulf today but too much shear still around and nothing really on deck that I can see in terms of possible formation.....But, if the moisture stays around, and, the shear drops over the next few weeks, you never know (that 36% chance alluded to by Dr. M)
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Quoting IKE:
Maybe 93L comes out of the GOM....6Z NAM


That AOI is already in the GOMEX. Check the satellites
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701. IKE
Maybe 93L comes out of the GOM....6Z NAM
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Bye bye, 92L...
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699. IKE
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT TUE JUN 2 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

A NON-TROPICAL AREA OF LOW PRESSURE LOCATED ABOUT 325 MILES NORTH-
NORTHEAST OF THE AZORES ISLANDS IS PRODUCING GALE-FORCE WINDS.
ALTHOUGH THE LOW HAS CHANGED LITTLE IN ORGANIZATION SINCE YESTERDAY
AND IS MOVING NORTHWARD OVER COOLER WATERS...IT WILL CONTINUE TO BE
MONITORED FOR SIGNS OF ADDITIONAL DEVELOPMENT. THERE IS A LOW
CHANCE...LESS THAN 30 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL
OR SUBTROPICAL CYCLONE DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER PASCH/BLAKE
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Quoting Thundercloud01221991:


what are they waiting for


Winds aren't just the only thing.

NHC seem to think it's not tropical enough, and not organised enough. Maybe looking for some consistency, though it seems it'll dissipate before that happens.

'
A NON-TROPICAL AREA OF LOW PRESSURE LOCATED ABOUT 275 MILES
NORTH-NORTHEAST OF THE AZORES ISLANDS IS PRODUCING WINDS TO NEAR
GALE FORCE. SHOWERS AND THUNDERSTORMS ASSOCIATED WITH THE LOW HAVE
CHANGED LITTLE IN ORGANIZATION OVER THE PAST FEW HOURS. THIS
SYSTEM IS EXPECTED TO MOVE NORTHWARD OVER COOLER WATERS DURING THE
NEXT DAY OR SO. THERE IS A LOW CHANCE...LESS THAN 30 PERCENT...OF
THIS SYSTEM BECOMING A SUBTROPICAL CYCLONE DURING THE NEXT 48 HOURS. '
Member Since: August 23, 2008 Posts: 7 Comments: 5300
I'll be on later.
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Quoting cg2916:
Have you looked at the SSD floaters? It may look ok on the visible, but the infrared images show it's very disorganized.


Yep........ Yesterday 92L looked like much more organized. GFS model was pointing to a warm core at 850 hPa. 92L yesterday had a similar appearance to VINCE (2005). Looking at its sustained wind intensity, perhaps should it be named as Subtropical Storm ANA?

Regards from Spain.
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Invest 92L won't be anything more than 92L, trust me.
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I'll be on chat too if anyone wants to be on.
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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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