Bill weakens, but still generating huge waves

By: Dr. Jeff Masters , 2:29 PM GMT on August 20, 2009

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Hurricane Bill has peaked in intensity, and now shows signs of weakening. Visible and infrared satellite imagery show that the hurricane is no longer as symmetric as it once was, with an oval instead of circular shape to its cloud pattern. Upper-level cirrus clouds are restricted on the storm's southwest side, indicating that upper-level winds from the southwest are shearing the storm. The University of Wisconsin CIMSS wind shear analysis shows about 10 - 15 knots of wind shear impacting Bill. The latest 8:18am EDT eye report from the Hurricane Hunters indicated that the eyewall had a gap in its southwest side, and the pressure had risen 2 mb since last night, to 951 mb. Maximum winds at the surface observed by the SFMR instrument were only Category 2 strength, though winds measured at the aircraft flight level of 10,000 feet still suggested Bill may be a Category 3 hurricane.

Wind shear is forecast to remain low to moderate, 5 - 15 knots, for the next three days, and it is possible Bill may see a relaxation of the wind shear affecting it, allowing re-intensification to Category 4 status. Sea Surface Temperatures (SSTs) will be plenty warm over the next three days, as Bill traverses a region of ocean with SSTs of 28 - 29°C. Total ocean heat content is at a maximum today, and will gradually decline over the next three days.


Figure 1. Visible satellite image of Bill at 1:33 pm EDT Thursday 8/20/09. Bill had an oval shape oriented SW - NE, and was missing upper-level cirrus clouds on the southwest side, indicating that wind shear from strong upper-level southwesterly winds was affecting it.

Water vapor satellite loops continue to show two small "short-wave" troughs of low pressure to the northwest of Bill, and these troughs are continuing to steer Bill to the northwest. The short wave troughs (so called because they have a relatively small amplitude and wavelength) are not strong enough to turn Bill due north, so Bill is expected to miss Bermuda. The official NHC forecast has the radius of tropical storm force winds from Bill barely reaching Bermuda on Saturday, so the island can expect sustained winds in the 35 - 45 mph range for a few hours on Saturday if the hurricane follows the NHC forecast track.


Figure 2. Visible satellite image of Bill's eye zoomed in, taken from NASA's Aqua spacecraft at 10:15am EDT Wednesday August 19, 2009. Image credit: NASA GSFC.

An unusually strong "long wave" trough of low pressure (called long wave because of its large amplitude and wavelength) is expected to develop along the U.S. East Coast this weekend. This trough will turn Bill to the north, and also bring high levels of wind shear in the 40 - 65 knot range on Sunday. The models have moved the forecast landfall point of Bill several hundred miles back and forth to the east and west over the past few days, but mostly agree that Cape Cod and Maine will probably miss a direct hit by Bill. However, these regions are still at the edge of Bill's cone of uncertainty, and a direct strike by Bill at Category 1 or 2 strength is a possibility. However, it is more likely that Bill will come ashore over the Canadian provinces of Nova Scotia or Newfoundland. Bill will be weakening rapidly as it makes landfall, and is likely to be a Category 1 hurricane if it hits Nova Scotia, or strong tropical storm if it hits Newfoundland. If Bill follows the official NHC forecast path, winds on Cape Cod and in eastern Maine are likely to remain below tropical storm force (below 39 mph).

Bill's waves
Hurricane Bill is generating huge waves, thanks to its enormous size and major hurricane intensity. Bill passed about 75 miles southwest of Buoy 41044 this morning, and the buoy recorded sustained winds of 67 mph, gusting to 92 mph, with a significant wave height (the height of the average 1/3 highest waves) of 38.8 feet. Output from NOAA's Wavewatch III model suggests that significant wave heights near Bill's center will peak at 50 feet by Saturday. Large swells from Bill will reach Bermuda this afternoon, increasing seas to 5 - 9 feet, according to the Bermuda Weather Service. Seas will increase to 10 - 20 feet on Friday and 20 - 30 feet on Saturday as Bill makes its closest approach to the island.

In the U.S., Bill's swells will reach New York's Long Island on Friday afternoon, and seas will build to 7 - 10' on Saturday and 12 - 16' on Sunday in the near shore waters. By Friday night, Bill's swells will be affecting the entire U.S. East Coast from Florida to Cape Cod. Maximum sea heights in near shore waters over the weekend will be about 7' from Florida to South Carolina, 11 - 14' along the North Carolina coast, 8 - 11' along the mid-Atlantic coast, and 10 - 11' along the coast of Maine. The highest waves along the U.S. coast will occur at Cape Cod, Massachusetts, where waves of 18 - 23' are being forecast by NOAA for Sunday. Bill's high waves are going to cause millions of dollars in erosion damage and create very dangerous rip currents and swimming conditions along the coast.

Hurricane History of Canada
Canada is no stranger to hurricanes, and receives a hit by a Category 1 or stronger hurricane several times per decade, on average. The most recent hurricane strike on Canada occurred in 2008, when Hurricane Kyle struck the southwestern tip of Nova Scotia, just north of Yarmouth. Kyle was rated a Category 1 hurricane with 75 mph winds at landfall, but damage was limited to uprooted trees, scattered power outages, and minor street flooding in Shelburne. The other hurricane to hit Nova Scotia this decade was much more serious. In 2003, Hurricane Juan made landfall at Halifax, Nova Scotia, as a Category 2 hurricane with 100 mph winds. A record storm surge of 4.9 feet inundated the city's waterfront, resulting in extensive flooding of the Halifax and Dartmouth waterfront properties. A buoy just outside Halifax Harbor measured a significant wave height of 9 meters (30 feet), and maximum wave heights of 20 meters (65 feet). Four people died in the storm. Juan downed a phenomenal number of trees--agriculture specialists estimate that 50 - 100 million trees blew down in Nova Scotia in two hours, with one million downed in Halifax alone. The Canadian Hurricane Center has a nice historical hurricane page with more information and photos.


Figure 3. Close up view of the damage at the Bedford Yacht Club after Hurricane Juan in 2003. Photo: Gary Dunbrack. Image credit: Environment Canada website on Hurricane Juan.

Elsewhere in the tropics
There are no threat areas in the Atlantic worth mentioning today, and no reliable models are calling for tropical cyclone development over the next seven days.

I'll have an update Friday morning.

Jeff Masters

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The eye has become much larger and more impressive and so has the structure over the last few hours.
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Bill kinda looks like he has a "mohawk" hairdo with that big chunk that's "broken" off his northwest corner. That's all from shear, right? What happens to those big chunks, do they just dissipate? Do they keep spinning with the storm?

Sorry for any silly questions, I'm still very new! Bill is the first storm I've paid such close attention to. I only moved to the NE US a few years ago. During the brief time I've lived here, this is the closest path I've seen yet, so I guess it just really captured my attention.
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Here is an interesting link to NASA about Bill.


http://www.nasa.gov/mission_pages/hurricanes/archives/2009/h2009_Bill.htmlNASA
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Quoting CloudGatherer:
Dropsonde in the eye just recorded 951mb at the surface, so at the very least, Bill has stopped weakening.
you can tell by looking at the ir satelite view. he is getting his round look again and the cirrus clouds are building back on the west side.
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Quoting scaldisnoel:
CloudGatherer,

Wasn't suggesting you specifically when I mentioned "JB haters", but there are some people who are unnecessarily derisive of what he has to say. He does tend to overpredict storms a bit, but much of what he says is suggesting the range of possibilities, from least destructive to most destructive. People tend to latch on to the most destructive possibility and say that he is predicting it with 100% guarantees, which isn't an accurate representation of what he is usually saying.


Fair enough. But there's a reason for that - if you elaborate on all potential paths of the storm in vivid detail, the one that'll stick in your audience's mind is the worst of them. And he has to know that. There's a reason why the NHC tends to float the possibility of landfall in its discussions well before it creeps into the advisories.

In unrelated news, a northeastern eyewall dropsonde just recorded surface-level winds of 110kts, and the aircraft has flight-level winds of 135kts. So we'll be back to 110kts for the 2PM advisory.

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Quoting NEwxguy:


It won't be to the dismay of me sitting here in eastern mass.


Hey NWwxguy!

No. Don't expect it would be :-)

I feel for low lying beach properties like the one in the photo posted by that lady recently. Depending on tides...could be a good amount of beachfront property damage even without wind...

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Quoting sfla82:
So I guess after all the wishcasting Bill will still follow the models and NHC forecast and be a fish just like forecasted...Bill didnt break through and head west or get push by any high pressures but did pretty much what was forecasted.....Maybe next time it will help from all the wishcasting...But I doubt it.

How would it be a fish storm if it hits Nova Scotia?
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@sfla82

This was from the last discussion, tell me what you think. Apparently the NHC's a bunch of wish casters too ;)

IT SHOULD BE NOTED THAT BILL WILL
PROBABLY NOT TURN AS SHARPLY BETWEEN 72-96 HR AS IMPLIED BY THE
TRACK GRAPHIC...AND THUS IS LIKELY TO PASS CLOSER TO NEW ENGLAND
THAN THE GRAPHIC WOULD SUGGEST.

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Latest dropsonde report...

168mph wind at 916mb

and a surface wind of 127mph!!!


Link
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With the dropsonde coordinates and the coordinates of the first TS flag and the first cat 1 flag, the radius of the windfield on the SW is:

TS winds - 134nm radius
Cat 1 winds - 22nm radius

This does not adjust for eyewall movement to the NW between the fixes, which would tend to OVERestimate the size of the fields.

It also does not provide, for obvious reasons, any effect of EWRC.

Pressure of 951 supports Cat 3.

Outbound winds in NE quadrant at least 90 knots (some flags missing on Google Earth) also supports low-end Cat 3 (96-113 knots). Wind speeds SFMR.
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I will have my new (2nd) blog in about 45 minutes at the most.
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Quoting CloudGatherer:


I don't hate the man, just the forecasts.

Bastardi consistently errs on the side of landfall. There's a method to his madness. He can be wrong ten times in a row, overestimating the storm's impact - but that only becomes clear after the storm has missed, and most people don't pay attention to forecasts at that point. But if he's right the eleventh time, if his catastrophic forecast seems more prescient than the NHC, that's the one that people will remember.

His forecasts prey upon human bias - we find it titillating to contemplate catastrophes (witness this very comments thread), and we tend to overemphasize extremely unusual events in assessing accuracy. It's just as probable that this hurricane will veer to the very eastern edge of the cone - yet I challenge anyone to find a Bastardi forecast which deviates outside of the cone in a manner that renders the storm irrelevant.

I won't be surprised to see his forecast hedge later today or tomorrow, and gradually inch back eastward. That's his other technique. Make the bold call now, walk it back later on, and point to the late-cycle forecast for evidence of his prescience and accuracy.

Thanks, but I'll stick with Dr. Masters.


Nailed it. Nailed it and a half.

Good luck telling the wishcasters that; they're too busy figuring out how Bill can land in Long Island Sound as a Cat 4 and Ana can come back to be a hurricane in the western GOMEX
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Quoting OSUWXGUY:


Good Morning WxLogic!

I agree that an easterly trend may now materialize...and to the dismay of some around here...

If I were a betting man...I would put money on the eastern side of the model consensus/NHC track. It's been my experience watching trough/recurving storm interaction that more often than not the storm ends up recurving harder/sooner


It won't be to the dismay of me sitting here in eastern mass.
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looks like the US East coast will have its deflector shield on for a month or so
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It hit the last point (or just slightly right of it)... that's a valid statement. However, given the movement since that last point, it is fair to say that if Bill continues said motion, he may miss the next point to the left.
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Quoting sfla82:
So I guess after all the wishcasting Bill will still follow the models and NHC forecast and be a fish just like forecasted...Bill didnt break through and head west or get push by any high pressures but did pretty much what was forecasted.....Maybe next time it will help from all the wishcasting...But I doubt it.



Maybe you should save this until after it has moved past the east coast??
Member Since: May 28, 2008 Posts: 38 Comments: 5303
Thanks for the easy to understand update StormW
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244. IKE
Quoting iluvjess:
Looks like Bill may miss the next forecat point to the West.


?

It's right on the tropical points and maybe a tad east of them.

Member Since: June 9, 2005 Posts: 23 Comments: 37860
Quoting HopquickSteve:


Agreed, Andrew was annoying. None of the sources we listened to predicted the left turn into Florida. That was a crappy Monday.
I was not living in Miami any longer but my parents were still living in the Kendall area. My father shot video when he went on the road (Dade County FD) and it was not a pretty sight. It is always best to keep a close eye on hurricanes if they are anywhere in the vicinity of where you live. Ivan was projected to pass N of Grand Cayman and it was a direct hit so I tend to watch what I am seeing rather than what the "models" are showing me.
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So I guess after all the wishcasting Bill will still follow the models and NHC forecast and be a fish just like forecasted...Bill didnt break through and head west or get push by any high pressures but did pretty much what was forecasted.....Maybe next time it will help from all the wishcasting...But I doubt it.
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Quoting StormW:
456,
Outstanding update!

How are you making out down there?


cant complain its been raining off and on for the past 2 days and we really need the rain
Member Since: July 24, 2005 Posts: 407 Comments: 19076
CloudGatherer,

Wasn't suggesting you specifically when I mentioned "JB haters", but there are some people who are unnecessarily derisive of what he has to say. He does tend to overpredict storms a bit, but much of what he says is suggesting the range of possibilities, from least destructive to most destructive. People tend to latch on to the most destructive possibility and say that he is predicting it with 100% guarantees, which isn't an accurate representation of what he is usually saying.
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We just finished teaching a Disaster Animal Response Team class in Nova Scotia! I hope everyone paid CLOSE attention in class!! Our thoughts are with all of those in the path of Bill and that they are making preparations now to evacuate and take their animals with them!
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238. IKE
Quoting CloudGatherer:


I don't hate the man, just the forecasts.

Bastardi consistently errs on the side of landfall. There's a method to his madness. He can be wrong ten times in a row, overestimating the storm's impact - but that only becomes clear after the storm has missed, and most people don't pay attention to forecasts at that point. But if he's right the eleventh time, if his catastrophic forecast seems more prescient than the NHC, that's the one that people will remember.

His forecasts prey upon human bias - we find it titillating to contemplate catastrophes (witness this very comments thread), and we tend to overemphasize extremely unusual events in assessing accuracy. It's just as probable that this hurricane will veer to the very eastern edge of the cone - yet I challenge anyone to find a Bastardi forecast which deviates outside of the cone in a manner that renders the storm irrelevant.

I won't be surprised to see his forecast hedge later today or tomorrow, and gradually inch back eastward. That's his other technique. Make the bold call now, walk it back later on, and point to the late-cycle forecast for evidence of his prescience and accuracy.

Thanks, but I'll stick with Dr. Masters.


That's exactly what he did with Katrina. He use to give his tropical forecasts on the Florida Network News. Local radio station here in Defuniak Springs,FL. carried FL. Network News and Bastardi's tropical outlooks. His forecast had Katrina hitting the Florida panhandle. Then when the models shifted west to LA. and Mississippi, so did he. I then heard him on Fox News saying he thought it was going to LA. and Mississippi all along.

No Joe...you didn't.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Dropsonde in the eye just recorded 951mb at the surface, so at the very least, Bill has stopped weakening.
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Quoting PcolaDan:
Question
Is the trough that is coming down and supposed to turn Bill normal in size and strength for this time of year? Or is this one of those like the ones earlier this summer that went all the way into the GoM and not typical? Made for some pleasant days here on the coast. I ask because if not a normal trough won't it be more easily influenced by other factors?


the trough is unusually large and strong for this time of year. which means it is less likely to be "busted" or anything like that.
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Quoting stormwatcherCI:
Not possible to be over blessed. Any year a hurricane doesn't make landfall in S Fla is a blessing. I know you are too young to remember Andrew.


Agreed, Andrew was annoying. None of the sources we listened to predicted the left turn into Florida. That was a crappy Monday.
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Quoting StormW:
Good afternoon!

I have an updated synopsis.

Thanks!

TROPICAL WEATHER SYNOPSIS /HURRICANE BILL/ AUG 20, 2009 ISSUED 12:30 P.M.

Thank you for the update. 15 foot wave
Quoting StormW:
Good afternoon!

I have an updated synopsis.

Thanks!

TROPICAL WEATHER SYNOPSIS /HURRICANE BILL/ AUG 20, 2009 ISSUED 12:30 P.M.

Interesting update, Storm. 21-25 foot waves in the bay of Maine! I'll try to get some pics. Gonna be staying in a hotel right by the coast in Portland.
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Quoting StormW:
Good afternoon!

I have an updated synopsis.

Thanks!

TROPICAL WEATHER SYNOPSIS /HURRICANE BILL/ AUG 20, 2009 ISSUED 12:30 P.M.


Great update. Thanks Storm.
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Quoting WxLogic:


A trend to the east appears to be shaping up... I believe the presence of shear will not allow Bill to have enough force to fight off the trough.


Good Morning WxLogic!

I agree that an easterly trend may now materialize...and to the dismay of some around here...

If I were a betting man...I would put money on the eastern side of the model consensus/NHC track. It's been my experience watching trough/recurving storm interaction that more often than not the storm ends up recurving harder/sooner
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Looks like Bill may miss the next forecat point to the West.
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Impressive

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting NRAamy:
hey PcolaDan!

:)



Hiya NRAamy
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Quoting scaldisnoel:
HHunter, be careful not to overstate what Joe Bastardi is saying, since there are some serious JB haters in here. My read on what he said in his most recent post is that Providence and Boston are probably out of the woods except for some gale force gusts and some heavy rain, unless Bill tracks more to the west than predicted. The Cape on the other hand, he seems to suggest, is quite likely to see, if not a direct hit, some hurricane force winds. He is more in line with the storm following the west side of the cone, or even a little west of that.


I don't hate the man, just the forecasts.

Bastardi consistently errs on the side of landfall. There's a method to his madness. He can be wrong ten times in a row, overestimating the storm's impact - but that only becomes clear after the storm has missed, and most people don't pay attention to forecasts at that point. But if he's right the eleventh time, if his catastrophic forecast seems more prescient than the NHC, that's the one that people will remember.

His forecasts prey upon human bias - we find it titillating to contemplate catastrophes (witness this very comments thread), and we tend to overemphasize extremely unusual events in assessing accuracy. It's just as probable that this hurricane will veer to the very eastern edge of the cone - yet I challenge anyone to find a Bastardi forecast which deviates outside of the cone in a manner that renders the storm irrelevant.

I won't be surprised to see his forecast hedge later today or tomorrow, and gradually inch back eastward. That's his other technique. Make the bold call now, walk it back later on, and point to the late-cycle forecast for evidence of his prescience and accuracy.

Thanks, but I'll stick with Dr. Masters.
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Question
Is the trough that is coming down and supposed to turn Bill normal in size and strength for this time of year? Or is this one of those like the ones earlier this summer that went all the way into the GoM and not typical? Made for some pleasant days here on the coast. I ask because if not a normal trough won't it be more easily influenced by other factors?
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Quoting stormwatcherCI:
Don't say for no reason. It is better to be safe than sorry. The stuff people buy from Home Depot won't spoil and IF the time comes when they do need it they might not be able to get it.
claudette did hit nw florida. so 2 out of three. and it is always better to be safe then sorry.
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It does not even matter what the models are showing.Anyone with some weather knowledge will recognize the fact that storms are dangerously unpredictable,especially tropical cyclones.A direct hit from a weak category-2 hurricane can bring life threatening situations anywhere.New England and the Mid Atlantic regions as we know are very populated areas and travel is difficult when the weather is good.I can surmise that if an evacuation order was given to late in a surge prone quadrant, people trying to leave could be trapped.
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Bill churns towards the northwest
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Well, it's been real.... but I gotta get going. Got some stuff that has to get done today. Prolly be able to check in again later in the p.m.

Have a good one! and all my Bermudian, Canadian and NE US brethren out there, be safe!
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Quoting NEVERRIGHT:
WELL SO FAR THEY HAD PEOPLE IN LIKE 30 DIFERENTS CITIES FREKING OUT AND SHOPPING AT HOME DEPOT AND LOWES FOR NO REASON AGAIN 3 STORMS IN THE PAST 6 DAYS AND NONE HIT ANYONE LOL
Don't say for no reason. It is better to be safe than sorry. The stuff people buy from Home Depot won't spoil and IF the time comes when they do need it they might not be able to get it.
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Quoting NEVERRIGHT:
WELL SO FAR THEY HAD PEOPLE IN LIKE 30 DIFERENTS CITIES FREKING OUT AND SHOPPING AT HOME DEPOT AND LOWES FOR NO REASON AGAIN 3 STORMS IN THE PAST 6 DAYS AND NONE HIT ANYONE LOL


Remove the caps please.
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hey PcolaDan!

:)

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Looks like Bill just went through an eyewall replacement cycle!

Smaller eye contracts then breaks apart leaving a broader eye. Probably means Bill is done weakening for now...

AVN Loop
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Quoting WeatherStudent:




Don't need to! I'm presently overly-blessed enough as it is right now.
Not possible to be over blessed. Any year a hurricane doesn't make landfall in S Fla is a blessing. I know you are too young to remember Andrew.
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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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