Leslie near hurricane strength; Son of Isaac (90L) emerges in the Gulf

By: Dr. Jeff Masters , 3:05 PM GMT on September 05, 2012

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Tropical Storm Leslie is growing more organized and is approaching hurricane strength on its slow voyage northwards at 2 mph towards the island of Bermuda. Moderately high wind shear of 15 - 20 knots due to strong upper-level winds out of the northwest continues to keep most of Leslie's heavy thunderstorms pushed to the east side of the storm, but satellite loops show that Leslie now has an impressive blow-up of heavy thunderstorms with cold cloud tops near its center. Leslie's slow forward speed means that the storm is staying over the cold water stirred up by the storm's winds, inhibiting intensification, but the waters underneath Leslie are warm to great depth, making this less of a factor than usual. According to the latest SHIPS model forecast, the shear is expected to fall steadily today, reaching the low category, 5 - 10 knots, by Thursday afternoon. Leslie is over warm ocean waters of 29 - 30°C, and the reduction in shear and warm waters should aid intensification, and potentially allow Leslie to be at Category 2 strength at its closest pass by Bermuda Saturday night and early Sunday morning, as indicated by the official NHC forecast. The latest 11 am EDT NHC wind probability forecast calls for a 48% chance that Leslie will be a Category 2 or stronger hurricane Sunday morning at 8 am EDT. Leslie is a huge storm, and tropical storm-force winds are expected to extend outward from its center 250 miles by Friday. Bermuda is likely to see a 42-hour period of tropical storm-force winds beginning Saturday morning near 2 am AST, and lasting until 8 pm AST Sunday night. The official NHC forecast shows Leslie nearly making a direct hit on Bermuda, and Leslie will be capable of bringing an extended period of hurricane-force winds lasting six or more hours to Bermuda Saturday night through Sunday morning, should a direct hit materialize. NHC is predicting that hurricane-force winds will extend outwards from the center of Leslie by 35 miles on Thursday night, and I expect this will increase to at least 60 miles by early Sunday morning, when Leslie will be making its closest pass by Bermuda.


Figure 1. Morning satellite image of Tropical Storm Leslie. Heavy thunderstorms have built near the center of the storm, and Leslie is near hurricane strength.

Leslie's impact on Canada
Leslie will stay stuck in a weak steering current environment until a strong trough of low pressure approaches the U.S. East Coast on Saturday. The timing of this trough is such that Leslie will be pulled northwards and then north-northeastwards over the weekend. There are still significant differences among the models in the timing and speed of Leslie's track over the weekend, but we can now dismiss the threat of Leslie making a direct hit on New England. The storm is likely to make landfall in Nova Scotia or Newfoundland, though there are significant differences in the models' predictions of the timing of Leslie's arrival in Canada. The GFS model predicts an early Tuesday landfall in Newfoundland, but the ECMWF model is much faster and farther west, predicting a Monday afternoon landfall in Nova Scotia. Large swells from Leslie are pounding the entire Eastern Seaboard, and these waves will increase in size as Leslie grows in strength this week. The Hurricane Hunters are scheduled to make their first flight into Leslie on Thursday afternoon.


Figure 2. Morning radar image of Invest 90L off the coast of the Florida Panhandle.

Son of Isaac: Invest 90L emerges in the Gulf of Mexico
During Tropical Depression Isaac's trek across the center of the U.S. during the Labor Day weekend, the storm was ripped in half. One portion of the storm moved over the Northeast U.S., bringing heavy rains there, and another portion sank southwards over Alabama. You can see this split by studying an animation of the vorticity at 850 mb (the amount of spin at low levels of the atmosphere, near 5,000 feet above sea level) from the University of Wisconsin. This remnant of Isaac, which still maintained some of Isaac's spin, brought heavy rains of 5 - 10 inches that caused flooding problems over portions of Alabama on Tuesday. The storm has now emerged over the Gulf of Mexico near the Florida Panhandle, and was designated Invest 90L this morning by NHC. In their 8 am Tropical Weather Outlook, NHC gave 90L a 20% chance of developing into a tropical depression by Friday morning. According to NHC naming rules, "if the remnant of a tropical cyclone redevelops into a tropical cyclone, it is assigned its original number or name". Since "the remnant" refers to the primary remnant, and 90L does not fit the definition of a "primary remnant", the storm will be given a new name should it develop into a tropical storm, according to information posted on the NHC Facebook page. Esau or Jacob--the names of the sons of the biblical Isaac--would be fitting names for 90L, but the next storm on the list of Atlantic storms is Nadine.

Long-range radar out of Mobile, Alabama shows a large area of heavy rainfall along the coast due to 90L. The echoes do show some spiral banding behavior, but there is only a slight evidence of rotation to the storm. Infrared satellite loops show that the thunderstorms associated with 90L are not that vigorous and do not have particularly cold cloud tops, and the area covered by the thunderstorms is relatively small. Wind shear is a high 20 - 30 knots over the northern Gulf of Mexico, but is predicted to fall to the moderate range, 10 - 20 knots, by Thursday afternoon. Ocean temperatures in the Gulf have been cooled down considerably by the passage of Hurricane Isaac last week, and are 28 - 28.5°C. This is still plenty warm enough to support formation of a tropical storm, and I expect 90L will increase in organization on Thursday and Friday as it moves slowly south or south-southwest. 90L could become a tropical depression as early as Thursday, though Friday is more likely. A hurricane hunter aircraft is scheduled to investigate 90L on Thursday afternoon. A trough of low pressure and an associated surface cold front will move southeastwards over the northern Gulf of Mexico on Sunday, and this trough should be capable of pulling 90L to the northeast to a landfall along the Florida Panhandle or west coast of Florida on Sunday.


Figure 3. Morning satellite image of Tropical Storm Michael.

Tropical Storm Michael in the Central Atlantic
Tropical Storm Michael has strengthened to 50 mph winds, and appears to have a favorable enough environment to become a hurricane later this week. Satellite loops show that this is a small tropical cyclone, far out over the open Atlantic, and none of the models show that Michael will threaten any land areas.

Elsewhere in the Atlantic
The GFS and ECMWF models are predicting that a new tropical wave due to move off the coast of Africa on Friday will develop into a tropical depression by the middle of next week. It's too early to tell if this system might threaten the Lesser Antilles Islands.

Jeff Masters

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Does anyone have links to any Bermuda webcams?
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new Nam at 84 hours
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Remnants of Isaac escape ridge in bad shape, never quite gets it together, well see if it survives to the atlantic
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Quoting dabirds:
Very weird to look at StL radar and see one line moving SE while hardly 50 Mi from it another line moving NW. Assume there's a high sitting over the city? Oh, and they had a 2.5 tremor 50 mi to the SE of town this am as well. Only two people had called w/in 30 minutes to say they felt it though.


The pictures they've been showing on St. Louis TV of the shelf cloud from that first line of storms are impressive. Got a good amount of rain and lightning off the weird back half coming from the southwest here in St. Peters.
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This is NOT good..sitting in the gulf for 4 days? GFS 96hrs
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Quoting Chicklit:
gosh spawn of Isaac dumping rain over New Orleans again.

unbelievable.



Partly cloudy skies here, the rain and dark skies are to the SE of NOLA over the coastal areas...
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Quoting islander101010:
.earthqk..ground.rolling.reported.from.samora.cnn

Yes, there are a lot of other places - BVI (3), Philippines, Indonesia, California (4), Taiwan, Hawaii, Solomon Islands, Mexico (2) Vanuatu and Costa Rica - have all had shakes today larger than 2.5 Link
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Reports of shaking coming in from all across Costa Rica and even as far north as San Salvador:



Reports so far indicate only minimal damage and no casualties.

A photo proportedly showing minor damage to a hospital:

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Quoting LargoFl:
..LOL can you imagine..old isaac circles around back to south florida..THEN..back into the gulf?....now THAT would be a first?


Let's not get too frisky yet. Those of us that have already been pounded by Isaac, and the ex-Isaac blob would like some time off now.
Member Since: October 2, 2004 Posts: 0 Comments: 15190
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Quoting 69Viking:
The Son of Isaac gave us another 3.5" of rain in the Fort Walton Beach area over the past couple of days and now the Doc thinks it might come back towards the Panhandle by the weekend, just what we don't need, more rain!
we got a months worth of rain in 6 hrs yesterday from the other half of isaac that passed over us



AWCN11 CWTO 051344
Updated weather summary for all of Southern Ontario and the
National Capital Region issued by Environment Canada
At 9:42 AM EDT Wednesday 5 September 2012.

------------------------------------------------- ------------
==weather event discussion==

It was a very wet day across portions of Southern Ontario Tuesday
with the rain being partially attributed to the added moisture from
the remnants of post tropical storm Isaac.

Tuesday morning began with thunderstorms which brought locally heavy
downpours during the morning commute, especially around the greater
Toronto area (gta). It morphed into a wide area of rain. It spread
across all of Eastern Ontario through the afternoon and evening.

A general rainfall amount of 40 mm of rain fell across the region
adjacent to the north shore of Lake Ontario with locally higher
amounts over 80 mm reported.

The following is a summary of the most significant rainfall reports
(mainly around the gta and north shore of Lake Ontario) Environment
Canada has received as of 1:00 AM.

Location rainfall amount (mm)
Lucan (near London) 50 (unofficial observation)
Kitchener 30 (unofficial observation)
university of Waterloo 39.5
Grimsby 39.8
Claireville dam (E of Brampton) 52.4
Stouffville dam (N of Markham) 87.3
Dufferin reservoir (Vaughan) 67.5
G ross lord dam reservoir 51.8
(Downsview)
Downsview 53.4 (as of 4 PM)
Buttonville airport (Markham) 104.0
Markham (milne dam) 49.2
Pearson airport 42.8
Downtown Toronto 34.3
Toronto (East York) 34.6 (as of 5 PM)
Brighton 45 (unofficial)
Trenton 78.6
Point Petre 98.2
Kingston 91
Stirling 41.6 (as of 5 PM)

Claireville, g ross lord dam, stouffville, Dufferin reservoir, and
Markham reports courtesy of the Toronto and region conservation
authority.

This weather summary contains preliminary information and may not
constitute an official or final report.

END/OSPC

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78 Hr
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Quoting LargoFl:
yes im afraid.so far it looks like it will take debby's path across the panhandle then across northern florida to the atlantic..just hope its a fast mover and doesnt stall out


The danged thing is moving SW but it's already started to set up what looks like reverse feed bands over the Panhandle, SE AL, and Georgia. This blob has a history of producing the heaviest rain away from the low with these reverse feeder bands. I wish it would hurry and die or something....
Member Since: October 2, 2004 Posts: 0 Comments: 15190
Quoting SFLWeatherman:
Is it going Back to S FL at 168HR??? lol
..LOL can you imagine..old isaac circles around back to south florida..THEN..back into the gulf?....now THAT would be a first?
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Quoting stormchaser19:
72 Hr


Remnants of Isaac abducted by the giant ridge..?
Its Debby all over again. :P
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Quoting sar2401:

yes.the.ground.does.have.a.tendency.to.roll.from. an. earthqk.thank.you.for.that.vital.information.


Is that really necessary?
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Quoting sar2401:

yes.the.ground.does.have.a.tendency.to.roll.from. an. earthqk.thank.you.for.that.vital.information.


Be nice.
If your spacebar was broken im sure you would enjoy.me.talking.like.this.to.you.too.
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Quoting RTSplayer:
90L is now analyzed at 1010mb, cauze it's over land and they got instruments on it.

Steering:

1000mb



990mb




It looks like 90L is going to merge with the naked LLC in the central gulf (any moment now) and will back up into the central or east-central gulf and get a head of steam worked up, before turning northeast and hitting Florida.


What the heck, it's the Gulf; I'll give it mid-level TS at least for the "landfall".
yes i think you could be right there
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72 Hr
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samarra.c.rica..georgia.sorry..getting.a.kybd.for.t he.birthday
Member Since: September 11, 2010 Posts: 1 Comments: 4589
Quoting islander101010:
.earthqk..ground.rolling.reported.from.samora

yes.the.ground.does.have.a.tendency.to.roll.from. an. earthqk.thank.you.for.that.vital.information.
Member Since: October 2, 2004 Posts: 0 Comments: 15190
Quoting 69Viking:
The Son of Isaac gave us another 3.5" of rain in the Fort Walton Beach area over the past couple of days and now the Doc thinks it might come back towards the Panhandle by the weekend, just what we don't need, more rain!


Yea, I was thinking the same. It gaves us 4" last night when it blew through. Just as everything was drying out from Isaac. Plus the rivers haven't even got back to normal yet. I wish if it does do anything it would go south and let us catch up but it doesn't look like it is going to cooperate.
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Quoting 69Viking:
The Son of Isaac gave us another 3.5" of rain in the Fort Walton Beach area over the past couple of days and now the Doc thinks it might come back towards the Panhandle by the weekend, just what we don't need, more rain!
yes im afraid.so far it looks like it will take debby's path across the panhandle then across northern florida to the atlantic..just hope its a fast mover and doesnt stall out
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Quoting islander101010:
.earthqk..ground.rolling.reported.from.samora.cnn


samoa?
thats far out no?
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Quoting islander101010:
.earthqk..ground.rolling.reported.from.samora.cnn


Looks like the crust is destabilizing across the globe
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Quoting RTSplayer:


"More Quickly" is the correct form.



i read it wrong. :P
oops, thanks
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60 Hr
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Quoting GeorgiaStormz:
Repost from previous blog:

. IT IS POSSIBLE THAT LESLIE COULD INTENSIFY MORE QUICKLY THAN
FORECAST FOR THE NEXT 48 HOURS OR SO..


I think the NHC should be in school, and I should be at the NHC


"More Quickly" is the correct form.

Member Since: January 25, 2012 Posts: 33 Comments: 1520
.earthqk..ground.rolling.reported.from.samora.cnn
Member Since: September 11, 2010 Posts: 1 Comments: 4589
48 Hr
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The Son of Isaac gave us another 3.5" of rain in the Fort Walton Beach area over the past couple of days and now the Doc thinks it might come back towards the Panhandle by the weekend, just what we don't need, more rain!
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gosh spawn of Isaac dumping rain over New Orleans again.

unbelievable.
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42 Hr
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Quoting European58:


Nadine, honey is that you?

Nadine must be quite old according to this video
Link
Guess I waited to long, but I'll let Chuck sing it when she forms, be it 90L or the next African wave, lol.
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You have to admire the tenacity of these smaller systems. Big burst circling the center currently.
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90L is now analyzed at 1010mb, cauze it's over land and they got instruments on it.

Steering:

1000mb



990mb




It looks like 90L is going to merge with the naked LLC in the central gulf (any moment now) and will back up into the central or east-central gulf and get a head of steam worked up, before turning northeast and hitting Florida.


What the heck, it's the Gulf; I'll give it mid-level TS at least for the "landfall".
Member Since: January 25, 2012 Posts: 33 Comments: 1520
Quoting SFLWeatherman:
Is it going Back to S FL at 168HR??? lol


It would be crazy, but ever more so after that back in the Gulf and anyone's guess from thereon out. WSVN is going to go bankrupt paying all those reporters overtime.
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Very weird to look at StL radar and see one line moving SE while hardly 50 Mi from it another line moving NW. Assume there's a high sitting over the city? Oh, and they had a 2.5 tremor 50 mi to the SE of town this am as well. Only two people had called w/in 30 minutes to say they felt it though.
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.
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Quoting CloudGatherer:
Nadine is a French variant of the Russian Nadia, itself derived from the word for 'Hope.'

I, for one, hope Isaac's daughter Nadine never gets herself together.


Nadine, honey is that you?

Nadine must be quite old according to this video
Link
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Two 7.6 quakes on either side of the Pacific in 6 days. Could we see another in the South Pacific soon?
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All times in GMT. Derived from NHC_ATCF data for TropicalStormLeslie at 5Sept12pm
KXFL-PalmCoast :: BDA-Bermuda ::


The bottom kinked line traces Leslie's path on its 4th day as a TropicalStorm
The middle kinked line traces Leslie's path on its 5th day
The top kinked line traces Leslie's path on its 6th day
Note the difference in the distances travelled by Leslie on its 4th, 5th, and 6th days
4th day: 204miles(329kilometres) @ ~8.5mph(13.7kmh)
5th day : 88miles (141kilometres) @ ~3.7mph ( 5.9kmh)
6th day : 60miles (097kilometres) @ ~2.5mph ( 4.0kmh)
The southernmost dot on the longest line is TS.Leslie's most recently reported position

The longest line is a straightline projection through TS.Leslie's 2 most recent positions to it's closest approach to Bermuda
4Sept.12pm: TS.Leslie had been headed for passage 126miles(202kilometres)East of Bermuda
4Sept.06pm: TS.Leslie had been headed for passage 86miles(139kilometres)WSWest of Bermuda
5Sept.12am: TS.Leslie had been headed for passage 238miles(383kilometres)SWest of Bermuda
5Sept.06am: TS.Leslie had been headed for passage 88miles(141kilometres)WSWest of Bermuda
5Sept.12pm: TS.Leslie was heading for passage 108miles(174kilometres)East of Bermuda

Copy&paste kxfl-29.404n81.094w, 32.387n62.5w, 31.7323n66.211w, 29.885n67.781w, 31.729n66.233w, 32.281n64.887w-bda-32.368n64.647w, 21.3n60.9w- 22.1n61.4w- 22.8n61.6w- 23.4n62.2w- 23.6n62.7w, 23.6n62.7w- 23.8n62.8w- 24.1n62.7w- 24.5n62.5w- 24.8n62.5w, 24.8n62.5w-25.0n62.6w, 25.0n62.6w-25.1n62.7w, 25.1n62.7w-25.3n62.8w, 25.3n62.8w-25.6n62.8w, 25.3n62.8w-32.382n62.8w, 32.368n64.647w-32.382n62.8w into the GreatCircleMapper for a larger map and other information
The previous mapping for comparison
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.
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Shakemap indicates strong to very strong shaking capable of producing moderate damage across much of the Nicoya Peninsula:



This is not a heavily populated region, but it's not empty either.
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Quoting SFLWeatherman:
Moderate, Tornadoes possible. Environment generally supports up to F1 intensity


It means a moderate risk of waterspouts, not tornadoes. They should have only done slight since in the legend text it has waterspouts, but it is pretty obvious since it is only over the water. In addition, this is the text from the HWO:
WATERSPOUTS: THE LOW LEVEL WIND PROFILE ACROSS THE GULF AND ATLANTIC WATERS WILL BE FAVORABLE FOR THE FORMATION OF WATERSPOUTS.
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Quoting sar2401:
Reposted from the previous blog. BTW, Doc, I like the Jacob and Esau analogy, but I don't think the NHC has a sense of humor about such things. :)

Yes, it would be Nadine. It appears to be fully over the Gulf now while still retaining its "blob" identity. There's a fair amount of convection, especially on the west side of te blob. It still looks like what we had here in Alabama over the ast three days. The low, such as it is, hasn't seemed to deepened dramatically, since it's 29.88 here in Montogmery and 29.84 from a bouy offshore. There's a weak high pressure to the north that is going to heat us up dramatically the next few days, probably forming a thermal trough over MS and AL. I have no idea what 90L will ultimately do but, since it was a big rainmaker over land, with lots of convection, it should be about the same over the Gulf. My best guess is that the blob moves east over central FL and is then absorbed in the existing trough over the east coast of FL. If the nascent low associated with the blob, which appears to be right over Pensacola, start to deepen significantly, it could be a TD at least.

This is truly a weird year. If the blob develops, how many times has an overland low ever got back in the Gulf and developed by coming straight down through MS and AL, with no other passage over water? I don't think there have been many.


It seems to be the year for BLOB storms reaking havoc. At least on the blog.
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27. 7544
new gfs should be interesting in a few more minutes
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Moderate, Tornadoes possible. Environment generally supports up to F1 intensity
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Quoting dabirds:
OK, just saw on Post Dispatch site, in article about storms passing through now, that they are now forecasting a high of 101 w/ 108 HI for StL - wow! Mets and Cards have to be happy they have a day game. At least it's only 70 at the moment there. Seems to be pushing a blob from the SW int the area behind the line that just pushed through to the SE. Guess after it gets through and sun pops it will heat up. Hope it stalls before it gets here. Get any drops from this ILwthr? Bet we got at least an inch.

90L is making the guy in my avatar want to sing, but I'll hold him off for now.
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Quoting Bobbyweather:

I heard it was a mistake; it was supposed to be issued for the Pacific but instead was mistakenly issued for the Caribbean.


Thats a heck of a mistake by the Pacific Tsunami office.
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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.