Dr. Jeff Masters' WunderBlog

Bill is gone; Invest 92 pops up

Posted by: Dr. Jeff Masters, 2:08 PM GMT on August 24, 2009

Hurricane Bill is no more. The hurricane swept past Canada's Nova Scotia province Sunday afternoon, then made landfall early this morning in southeastern Newfoundland as a borderline tropical storm/Category 1 hurricane. Bill's waves claimed two lives over the weekend, a 54-year old swimmer that drowned in Florida, and a 7-year old girl in Maine that got swept into the sea by a big wave. The first death of the 2009 Atlantic hurricane season occurred on August 16, when a swimmer drowned in the rough surf from Tropical Storm Claudette at Pananma City Beach, FL.

Nova Scotia misses a direct hit
The center of Bill scooted parallel to the coast of Nova Scotia Sunday afternoon, and never quite came onshore. Since the storm's forward speed was so rapid--about 35 mph--this resulted in a highly asymmetric wind distribution. Since the top winds of a hurricane include the forward motion of the storm, Bill's top winds of 85 mph observed in the offshore, right front quadrant of the storm meant that the winds on the weak side of the storm, over Nova Scotia, were 85 mph minus 35 mph, or just 50 mph. Winds along most of the coast stayed below 39 mph, the borderline for tropical storm-force winds. The strongest winds measured in Canada were at Sable Island, which lies 150 miles offshore of Nova Scotia. Winds on the island hit 61 mph, gusting to 77 mph, between 4 - 5 pm ADT Sunday afternoon. A few islands along the Nova Scotia coast, such as Beaver Island and Hart Island, reported sustained winds of 39 - 40 mph. The big story for Nova Scotia was the waves from Bill. Buoy 44258 at the mouth of Halifax Harbor recorded significant wave heights of 29.5 feet and maximum wave heights of 49 feet as Bill passed 50 miles offshore. The buoy recorded top sustained winds of 35 mph, gusting to 51 mph. The waves combined with a 1.5 - 3 foot storm surge flooded many coastal roads. Buoy 44150, about 160 miles offshore of of the southwest tip of Nova Scotia, was in the east eyewall of Bill between 10 - 11 am ADT, and reported sustained winds of 62 mph, gusting to 85 mph, with significant wave heights of 44 feet. The buoy recorded a maximum wave height of 87 feet, according to Environment Canada. The highest official rain report on Nova Scotia was 2.6" (65 mm) at Yarmouth. Rainfall cause some localized flooding and road damage. Bill's winds cut power to about 40,000 people at the height of the storm. At Peggys Cove, three men were hit by a giant wave but were not hurt. A gift shop and attached home in the village were swept off of their foundation.

Newfoundland gets hit, but damage is minor
The southeast corner of Newfoundland took a direct hit from Bill. The storm made landfall early this morning as a borderline tropical storm/Category 1 hurricane. Top winds on the island were measured at Cape Race, which recorded sustained winds of 58 mph, gusting to 76 mph, between 1:30 and 2:30 am NDT. A storm surge of 1.2 meters (4 feet) was estimated by Environment Canada for Placentia Bay where Bill made landfall. Damage was minor on Newfoundland, with no major flooding reported. Bill dumped up to three inches of rain on Newfoundland.

Figure 1. The eye of Hurricane Bill on August 19 at 2157 UTC, from a NOAA P-3 Hurricane Hunter aircraft flying at 10,000 feet. Photo credit: Jack Parrish of NOAA's Aircraft Operations Center.

Kelvin-Helmholtz instability waves in the eye of Bill
Flight Director Jack Parrish of NOAA's Aircraft Operations Center snapped a cool photo in the eye of Hurricane Bill on Friday, showing the existence of a Kelvin-Helmholtz instability wave (Figure 1). The photo was taken on August 19 at 2157 UTC, from a NOAA P-3 Hurricane Hunter aircraft flying at 10,000 feet. The photo is taken looking WNW towards the eyewall. The towering clouds of the eyewall extend up to 50,000 - 55,000 feet in the photo, and the ocean surface is not visible, due to stratocumulus clouds covering the bottom of the eye. The center of the photo shows that the top of one of these stratocumulus clouds has a feature that looks like a breaking wave in the ocean. Well, that is an example of a breaking wave in the atmosphere known as a Kelvin-Helmholtz instability wave. The atmosphere behaves as a fluid, and thus has wave-like motions. When there is a sudden change of wind speed along the top of a cloud (wind shear), the flow can become unstable and cause breaking waves to form. One can see Kelvin-Helmholtz in the sky several times per year, and several alert wunderphotographers have uploaded photos of these waves over the years. However, it is uncommon to see these waves in the stratocumulus clouds covering the eye of a hurricane.

Figure 2. Water vapor satellite image for 8:15 am EDT 8/24/09. A tropical wave is approaching the Northern Lesser Antilles Islands, but is running into high wind shear from an upper-level cold low to the west of it. Image credit: NOAA/SSD.

Tropical wave approaching Lesser Antilles becomes Invest 92
A tropical wave with a moderate amount of shower activity is moving west-northwest at 20 - 25 mph and is approaching the northern Lesser Antilles Islands. This wave was designated "Invest 92" (92L) by NHC this morning. The wave is under about 20 - 30 knots of wind shear due the strong upper-level winds from the west. These winds are being created by the counter-clockwise flow of air around an upper-level cold-cored low north of Puerto Rico (Figure 2). This low is expected to move west-southwest and slowly weaken over the next two days, allowing shear to drop to the moderate 10 - 20 knot range beginning Tuesday night, according to the SHIPS model. By Wednesday, the upper low is predicted to be weak enough and far enough away from 92L that it will have a chance to develop. Most of the models show some degree of development of 92L by Thursday, when it is expected to be a few hundred miles off the coast of South Carolina. This wave could turn northward and give a wet weekend to New England, though it is too early to be confident of this. NHC is giving 92L a low (less than 30% chance) of developing into a tropical depression by Wednesday morning. The upper-level low will create plenty of wind shear and dump cold, dry air into 92L over the next two days, so Wednesday is probably the earliest we can expect the system to begin organizing into a tropical depression.

Several models predict the development of a tropical wave coming off the coast of Africa late this week.

I'll have an update Tuesday.

Jeff Masters

Beach Wall wave 1 (BeachBecky)

Waves from Hurricane Bill crashing on the sea wall during high tide in Lynn, MA

Hurricane Bill Waves Day 2 # 9 (RIWXPhoto)

Kelvin-Helmholtz Instabilities (btangy)

Kelvin-Helmholtz Instabilities to the S of Boston. Wavy like pattern in clouds is caused by a difference in winds between the cloud layer and the layer just above (called wind shear). The manifestation of this at the top of the altostratus deck is quite a beautiful and rare sight!

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851. futuremet 10:29 PM GMT on August 24, 2009
Quoting Vortex95: Drak can you clarify, when you saying all of the GOM states except Florida are you saying the GOM side of Florida,has a chance of being affected? No, he likely meant the east coast. Member Since: July 19, 2008 Posts: 43 Comments: 4049

852. bwat 10:29 PM GMT on August 24, 2009
Quoting Dakster: Going by what has happened in recent previous seasons. (I know this is bad, as past performance doesn't gaurantee future performance) It seems like multiple Hurricanes take roughly the same path throughout the season. Notice I did not say ALL OF THEM DO, just that numerous ones do. For example last years straight west runs across the Atlantic and into Mexico, and in 2004 and 2005 , the multiple Florida strikes. So, Ike, you comment on Bill Part 2 seems very reasonable to me at the moment, going by nothing but historical reference at the moment. You have a point, remember 96 with Bertha and Fran, they made landfall in almost the same location only about a month apart if I remember correctly. Member Since: August 18, 2009 Posts: 0 Comments: 338

854. Tazmanian 10:30 PM GMT on August 24, 2009
Quoting Vortex95: Drak can you clarify, when you saying all of the GOM states except Florida are you saying the GOM side of Florida,has a chance of being affected? he said Florida northward should monitor the progression of this system. Member Since: May 21, 2006 Posts: 5088 Comments: 111306

855. 7544 10:34 PM GMT on August 24, 2009
way too early to tell but if the high does get stonger and 92l gets seperated from the ull thats pulling it along by trying to detach its self we can see a whole new ball game in play Member Since: May 6, 2007 Posts: 0 Comments: 5921

856. Drakoen 10:33 PM GMT on August 24, 2009
Quoting futuremet: Drak, the problem with this, is that we have a relatively short amount of time to monitor this system. The models are expecting a tropical cyclone to form near the Bahamas as early as 48hrs. The anomalously complex upper level set up making this inconvenient for forecasters. As a result of the remarkable credibility the ECMWF has acquired this year, I am leaning toward its forecasts. I am leaning with the ECMWF in the system missing the first weakness and bringing it into the western Bahamas. A lot of this looks like timing issue too. When the upper level trough splits and an upper level cyclone forms and moves into the GOM and begins to advect eastward. Member Since: October 28, 2006 Posts: 57 Comments: 29010

857. mobilegirl81 10:34 PM GMT on August 24, 2009
El nino....and we are looking at a favorable pattern with trade winds forecasted to relax substantially. This is getting interesting. Hope the NHS is ready to take notes. Member Since: August 31, 2008 Posts: 0 Comments: 833

858. Cavin Rawlins 10:35 PM GMT on August 24, 2009
93L and 92L - I'm in favor of 92L Member Since: July 24, 2005 Posts: 407 Comments: 19076

859. scCane 10:35 PM GMT on August 24, 2009
From charleston national weather service discussion Long term /Wednesday through Monday/... the period will start off with a closed off upper low over the Gulf states...generally zonal upper flow well north of the area from the Great Lakes region to New England. A weakening deep layer ridge will be over the east central Atlantic waters. The big question for at least the first part of the extended period will be the potential for the development of a tropical system somewhere north-northeast of the Bahamas and south of 30 degree north latitude by Thursday. The models are not in very good agreement on the development...timing...or placement of this potential system. The GFS seems to be the weakest and furthest east with this system...keeping it well east of our region...while the European model (ecmwf) and NAM seem to be indicating the potential for the developing low center to move farther west...closer to the southeast U.S. Coast. Given the large uncertainty with the potential evolution of this system....stay tuned to the latest forecasts and discussions from the National Hurricane Center and our office. Overall...made very little change to the previous forecast. Deep layer moisture increases to near 2 inches by Wednesday...and sticks around through about Saturday. The closed upper low is still shown to begin ejecting NE toward the area on Thursday...then move across the region Friday and into early Saturday. The latest guidance continues to show higher probability of precipitation for the Thursday and Friday periods...and have nudged forecast probability of precipitation up a tad for these time frames. Think given the available moisture and lift from the upper trough...we should see at least chance/scattered mainly afternoon convection. However...this scenario hinges on the idea that the developing Atlantic tropical low mentioned above stays well east of the region. Previous model forecasts even suggested that the region would actually remain rather dry through this week as the moisture with the tropical low remained well east and the lift/moisture with the upper low stayed just west of the forecast area. Confidence on this solution is beginning to fall rapidly...and have therefore begun to trend probability of precipitation up slightly for at least Thursday and Friday. Models are now showing the potential for a decent frontal passage by the end of the period. The GFS is showing a cold front moving through on Monday...while the European model (ecmwf) is slower...showing a front on Tuesday. Too early yet to have much confidence on this feature...and have therefore maintained slt chance to chance diurnal probability of precipitation for Monday. Member Since: May 9, 2007 Posts: 0 Comments: 152

860. BahaHurican 10:36 PM GMT on August 24, 2009
Quoting Drakoen: I am leaning with the ECMWF in the system missing the first weakness and bringing it into the western Bahamas. A lot of this looks like timing issue too. When the upper level trough splits and an upper level cyclone forms and moves into the GOM and begins to advect eastward. Starting to feel a bit queazy here... Member Since: October 25, 2005 Posts: 19 Comments: 17588

861. Drakoen 10:37 PM GMT on August 24, 2009
Quoting Vortex95: Drak can you clarify, when you saying all of the GOM states except Florida are you saying the GOM side of Florida,has a chance of being affected? Just the east coast of Florida has a chance at being affected. The model unanimously agree on a cut-off mid to upper level cyclone in the GOM. The timing of this and the storm's relative position are the problem. Member Since: October 28, 2006 Posts: 57 Comments: 29010

862. trunkmonkey 10:38 PM GMT on August 24, 2009
your right Drakoen, we don't have all the answers regarding storms Member Since: August 18, 2007 Posts: 0 Comments: 463

863. largeeyes 10:39 PM GMT on August 24, 2009
If NBC calls the wave that killed the 7 year old "rogue" one more time....... Member Since: August 22, 2006 Posts: 0 Comments: 1379

865. IKE 10:42 PM GMT on August 24, 2009
18Z NOGAPS.....keeps 92L just off-shore the east coast of the USA. Has 93L firing up in the east-Pac. Shows another strong trough heading into the SE USA on the end of the run. Member Since: June 9, 2005 Posts: 23 Comments: 37044

866. 7544 10:42 PM GMT on August 24, 2009
Quoting Drakoen: Just the east coast of Florida has a chance at being affected. The model unanimously agree on a cut-off mid to upper level cyclone in the GOM. The timing of this and the storm's relative position are the problem. possible so you think the next run the models will agree with the model 456 posted above Member Since: May 6, 2007 Posts: 0 Comments: 5921

867. Dakster 10:42 PM GMT on August 24, 2009
Quoting largeeyes: If NBC calls the wave that killed the 7 year old "rogue" one more time....... Yeah really... I think it is rogue reporting that is doing us all in. Member Since: March 10, 2006 Posts: 0 Comments: 4918

868. Tazmanian 10:42 PM GMT on August 24, 2009
the E PAC has all most seen 9 name storms this AUG Member Since: May 21, 2006 Posts: 5088 Comments: 111306

869. largeeyes 10:43 PM GMT on August 24, 2009
Does any model NOT develop 92L? Member Since: August 22, 2006 Posts: 0 Comments: 1379

870. jipmg 10:43 PM GMT on August 24, 2009
Quoting largeeyes: Does any model NOT develop 92L? yes

872. VAbeachhurricanes 10:45 PM GMT on August 24, 2009
Quoting largeeyes: Does any model NOT develop 92L? GFDL Member Since: September 6, 2007 Posts: 0 Comments: 4797

873. yellowpine 10:45 PM GMT on August 24, 2009
Jeff Masters' post discussing the weak and strong sides of rapidly-moving Hurricane Bill remind me of a question I have had for a long time. When the hurricane center says the highest winds in a hurricane are 75 mph, is that the wind an observer on the ground would experience on the strong side of the storm, or would you have to start with 75 mph and add or subtract the forward motion of the storm to get your personal wind? If a storm that was moving forward at 20 mph suddenly became stationary, would its maximum winds be dropped by 20 mph?

874. klaatuborada 10:47 PM GMT on August 24, 2009
Quoting largeeyes: If NBC calls the wave that killed the 7 year old "rogue" one more time....... Time to write a letter! LOL! Member Since: August 15, 2004 Posts: 23 Comments: 380

876. extreme236 10:49 PM GMT on August 24, 2009
Quoting Tazmanian: the E PAC has all most seen 9 name storms this AUG Current activity is still near-below average. Member Since: August 2, 2007 Posts: 19 Comments: 19234

877. amd 10:49 PM GMT on August 24, 2009
Quoting yellowpine: Jeff Masters' post discussing the weak and strong sides of rapidly-moving Hurricane Bill remind me of a question I have had for a long time. When the hurricane center says the highest winds in a hurricane are 75 mph, is that the wind an observer on the ground would experience on the strong side of the storm, or would you have to start with 75 mph and add or subtract the forward motion of the storm to get your personal wind? If a storm that was moving forward at 20 mph suddenly became stationary, would its maximum winds be dropped by 20 mph? The NHC used to determine maximum winds by the latter classification: what would the maximum winds be if the storm was stationary. However, currently the NHC lists any 1-min maximum substained wind, irrespective of any movement, as its maximum wind. Not sure when this was changed however. Member Since: August 29, 2005 Posts: 0 Comments: 1024

878. BahaHurican 10:50 PM GMT on August 24, 2009
ROGUE: isolated, aberrant, dangerous, or uncontrollable Like a rogue elephant, like a scoundrel, or other dishonest person Member Since: October 25, 2005 Posts: 19 Comments: 17588

879. 21N71W 10:50 PM GMT on August 24, 2009
Evening All, Baha I need your thoughts please.... Member Since: August 1, 2006 Posts: 0 Comments: 180

880. BahaHurican 10:51 PM GMT on August 24, 2009
Geez. Head hitting the keyboard here. Not used to these 5 a.m. wakeups anymore..... BBL. Keep an eye on 92L for me.... Member Since: October 25, 2005 Posts: 19 Comments: 17588

881. presslord 10:54 PM GMT on August 24, 2009
Quoting Drakoen: I am leaning with the ECMWF in the system missing the first weakness and bringing it into the western Bahamas. A lot of this looks like timing issue too. When the upper level trough splits and an upper level cyclone forms and moves into the GOM and begins to advect eastward. ...so...Cat 5...and Charleston is obliterated? Member Since: August 13, 2007 Posts: 0 Comments: 10377

883. CatastrophicDL 10:57 PM GMT on August 24, 2009
Press someone accused me today of stealing one of your hats :o) Member Since: September 3, 2007 Posts: 3 Comments: 1519

884. presslord 10:56 PM GMT on August 24, 2009
Quoting CatastrophicDL: Press someone accused me today of stealing one of your hats :o) looks good on ya... Member Since: August 13, 2007 Posts: 0 Comments: 10377

887. largeeyes 11:01 PM GMT on August 24, 2009
Yikes, that CMC would make me run out for some supplies..... Member Since: August 22, 2006 Posts: 0 Comments: 1379

889. mobilegirl81 11:05 PM GMT on August 24, 2009
The trade winds are forecast to relax, early to mid September over the tropical Atlantic.. Member Since: August 31, 2008 Posts: 0 Comments: 833

891. stormpetrol 11:06 PM GMT on August 24, 2009
I see we now have 93L, all the models sames to be taking it into the EPAC, if by some outside chance it skirts the east coast of Nicaragua and goes through the yucatan channel could be a whole other ball game, this might be the one to watch imo. Member Since: April 29, 2007 Posts: 0 Comments: 6394

892. klaatuborada 11:06 PM GMT on August 24, 2009
Cape Cod - For the first time in months weather is coming down out of the NW. The jet stream/high pressure system is finally affecting our weather. Instead of storms going to our West traveling North and missing us, they are coming in from North heading SouthEast and missing us. T-storms predicted either too far North going out to sea or dissipating prior to arrival. Typical. Still muggy, but better. Depending on timing, 92L may get pulled up as the high moves through and out. Too early to tell of course. This is going to be an interesting Aug/Sept/Oct. Need to go finish dinner. I'll be in and out lurking. Member Since: August 15, 2004 Posts: 23 Comments: 380

893. canesrule1 11:07 PM GMT on August 24, 2009
I think 92L will be moving in it's current general direction then turn northward scrapping EFLA.

894. Skyepony (Mod) 11:07 PM GMT on August 24, 2009
Wow 93L. The blob I gave an outside chance of developing a little once it came off N end of South America a day or two ago, that would move west & hit C America. I think it's hay day still will be in EPAC. Member Since: August 10, 2005 Posts: 144 Comments: 29234

895. TampaSpin 11:08 PM GMT on August 24, 2009
Quoting presslord: looks good on ya... Time to dig a hole and hunker down PRESS....LOL Member Since: September 2, 2007 Posts: 175 Comments: 19747

896. indianrivguy 11:09 PM GMT on August 24, 2009
evening Senior Chief Member Since: September 23, 2006 Posts: 1 Comments: 1777

897. DaytonaBeachWatcher 11:09 PM GMT on August 24, 2009
Quoting presslord: ...so...Cat 5...and Charleston is obliterated? not just charleston, the whole CAROLINAS Member Since: June 29, 2007 Posts: 0 Comments: 1125

898. stormsurge39 11:10 PM GMT on August 24, 2009
Does it look like 92L is organizing more around the center of circulation?

899. hurricane556 11:10 PM GMT on August 24, 2009
Quoting stormsurge39: Does it look like 92L is organizing more around the center of circulation? it seems you are correct Member Since: July 16, 2008 Posts: 0 Comments: 253

900. canesrule1 11:10 PM GMT on August 24, 2009
Don't think 93L will become of anything over the atlantic, imo, might become a hurricane over the EPAC according to SHIPS intensity model initialized at 2 PM. -CanesRule1.

901. TampaSpin 11:11 PM GMT on August 24, 2009
I guess NHC declared 93L because it looks pretty. It does not have a chance to become anything before going onshore.... Member Since: September 2, 2007 Posts: 175 Comments: 19747

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