TROPICAL STORM SEAN

[dkmac]

70% chance of another storm.

[h=1]November Atlantic hurricane outlook[/h]By Dr. Jeff Masters

Published: 9:35 AM CDT on November 01, 2011
Hurricane Rina is gone, and the tropical Atlantic is quiet, with no threat areas to discuss, and no models predicting development of a tropical depression during the coming seven days. So, are we all done for 2011? Or will this seventh-busiest hurricane season of all-time spawn a Tropical Storm Sean? Let's try and come up some answers. Since the active hurricane period we are in began in 1995, ten of the sixteen years (62%) have seen one or more Atlantic named storms form after November 1, for a total of fifteen late-season storms:

2009: Hurricane Ida on November 4
2008: Hurricane Paloma on November 6
2007: Tropical Storm Olga on December 11
2005: the "Greek" storms Gamma, Delta, Epsilon, and Zeta
2004: Tropical Storm Otto on November 29
2003: Odette and Peter in December
2001: Hurricane Noel on November 5 and Hurricane Olga on November 24
1999: Hurricane Lenny on November 14
1998: Hurricane Nicole on November 24
1996: Hurricane Marco on November 19

Only three of these storms (20%) caused loss of life: Hurricane Ida of 2009, which killed one boater on the Mississippi River; Tropical Storm Odette of 2007, whose floods killed eight people in the Dominican Republic; and Hurricane Lenny of 1999, which killed fifteen people in the Lesser Antilles. "Wrong-way Lenny" was both the deadliest and the strongest November hurricane on record (Category 4, 155 mph winds). There have been only seven major Category 3 or stronger hurricanes in the Atlantic after November 1. Part of the reason for the relatively low loss of life for November storms is that they tend to form from extratropical low pressure systems that get cut off from the jet stream and linger over the warm waters of the subtropical Atlantic. These type of systems typically get their start in the middle Atlantic, far from land, and end up recurving northeastwards out to sea. However, as I noted in the wake of last year's Hurricane Tomas last November in my blog post, Deadly late-season Atlantic hurricanes growing more frequent, It used to be that late-season hurricanes were a relative rarity--in the 140-year period from 1851 - 1990, only 30 hurricanes existed in the Atlantic on or after November 1, an average of one late-season hurricane every five years. Only four major Category 3 or stronger late-season hurricanes occurred in those 140 years, and only three Caribbean hurricanes. But in the past twenty years, late-season hurricanes have become 3.5 times more frequent--there have been fifteen late-season hurricanes, and five of those occurred in the Caribbean. Three of these were major hurricanes, and were the three strongest late-season hurricanes on record. Dr. Jim Kossin of the University of Wisconsin published a 2008 paper in Geophysical Research Letters titled, "Is the North Atlantic hurricane season getting longer?" He concluded that yes, there is an "apparent tendency toward more common early- and late-season storms that correlates with warming Sea Surface Temperature but the uncertainty in these relationships is high". The recent increase in powerful and deadly November hurricanes would seem to support this conclusion.


Figure 1. The strongest hurricane on record in the Atlantic in November, Hurricane Lenny, takes aim at the Lesser Antilles on November 17, 1999. Image credit: NOAA.

Forecast for November 2011
The oceans are certainly warm enough to support continued development of tropical cyclones. Sea Surface Temperatures (SSTs) over a wide area of the tropical Atlantic are 0.5 - 1.0°C above average, and are well above the 26°C (79°F) threshold typically needed to support tropical storm formation (Figure 2.) However, wind shear is starting to rise over much of the tropical Atlantic as the jet stream moves farther south in its usual seasonal cycle. Wind shear over most of the Atlantic will be too high to support tropical storm formation over the coming two weeks, according to the latest run of the GFS model (Figure 3.) Only the southern Caribbean and a few transient pockets in the middle Atlantic east and southeast of Bermuda will have low enough wind shear to support tropical storm formation over the next two weeks. The African Monsoon is quiet this time of year, and we no longer have African waves coming off the coast of Africa that can act as the seeds for formation of a tropical storm in the Caribbean. If we do get a tropical storm, it will probably be to the northeast of the Lesser Antilles, far from land, in a region where an extratropical low pressure system gets cut off from the jet stream and lingers long enough over warm waters to acquire tropical characteristics and get a name. Both the GFS and ECMWF models are suggesting a system like this may take form 7 - 10 days from now. Taking all these factors into account, I predict we are all done this hurricane season with storms that will cause loss of life, but there is still a 70% chance that we will get one or more named storms in the middle Atlantic that will stay out to sea and not affect land.


Figure 2. Sea surface temperatures in the Atlantic on November 1, 2011. The black dotted line is the 26°C (79°F) isotherm, which marks the boundary where tropical storm formation can typically occur. A large portion of the Atlantic is still capable of supporting tropical storm formation.


Figure 3. Wind shear forecast for November 11, 2011, as predicted by the 2am EDT November 1, 2011 run of the GFS model. The model is predicting low wind shear of less than 4 m/s (about 8 knots, light red colors) in the southern Caribbean and southern Lesser Antilles Islands. Very high wind shear in excess of 44 m/s (85 knots, orange colors), associated with the jet stream, will protect regions north of the Caribbean.

I'll have a new post Wednesday or Thursday.

Jeff Masters

[corky]

It ain't over yet.

two_atl.gif

http://www.nhc.noaa.gov/

[ROLLTIDE]

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AL, 98, 2011110612, , BEST, 0, 283N, 684W, 45, 1005, EX, 34, NEQ, 400, 0, 0, 400, 1012, 300, 180, 0, 0, L, 0, , 0, 0, INVEST, S,

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BEGIN
NHC_ATCF
invest_al982011.invest
FSTDA
R
U
040
010
0000
201111060600
NONE
NOTIFY=ATRP
END
INVEST, AL, L, , , , , 98, 2011, DB, O, 2011110606, 9999999999, , , , , , METWATCH, , AL982011
AL, 98, 2011110506, , BEST, 0, 330N, 738W, 45, 1005, EX, 34, NEQ, 450, 100, 200, 450,
AL, 98, 2011110512, , BEST, 0, 312N, 725W, 45, 1005, EX, 34, NEQ, 425, 0, 175, 425,
AL, 98, 2011110518, , BEST, 0, 298N, 711W, 45, 1005, EX, 34, NEQ, 400, 0, 175, 400,
AL, 98, 2011110600, , BEST, 0, 287N, 698W, 45, 1005, EX, 34, NEQ, 400, 0, 160, 400, 0, 0, 160, 0, 0,
AL, 98, 2011110606, , BEST, 0, 282N, 688W, 45, 1005, EX

[ROLLTIDE]

[dkmac]

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
700 AM EST SUN NOV 6 2011

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

1. A NON-TROPICAL LOW PRESSURE SYSTEM LOCATED ABOUT 350 MILES
SOUTHWEST OF BERMUDA IS PRODUCING A LARGE AREA OF GALE-FORCE
WINDS OVER THE WEST-CENTRAL ATLANTIC. ALTHOUGH THE ASSOCIATED
SHOWERS AND THUNDERSTORMS ARE CURRENTLY DISORGANIZED...THE LOW
COULD GRADUALLY ACQUIRE SUBTROPICAL CHARACTERISTICS AS IT MOVES
OVER WARMER WATER DURING THE NEXT COUPLE OF DAYS. THIS SYSTEM HAS
A LOW CHANCE...10 PERCENT...OF BECOMING A SUBTROPICAL CYCLONE
DURING THE NEXT 48 HOURS AS IT DRIFTS GENERALLY SOUTHWARD.
ADDITIONAL INFORMATION ON THIS GALE AREA CAN BE FOUND IN HIGH SEAS
FORECASTS ISSUED BY THE NOAA NATIONAL WEATHER SERVICE UNDER AWIPS
HEADER NFDHSFAT1...AND UNDER WMO HEADER FZNT01 KWBC.

[dkmac]

1AM

A NON-TROPICAL LOW PRESSURE SYSTEM LOCATED ABOUT 400 MILES
SOUTHWEST OF BERMUDA CONTINUES TO PRODUCE GALE-FORCE WINDS OVER
A LARGE PORTION OF THE WEST-CENTRAL ATLANTIC. THUNDERSTORM ACTIVITY
HAS DEVELOPED CLOSER TO THE SURFACE CENTER DURING THE PAST SEVERAL
HOURS...AND IF THIS TREND CONTINUES...THE LOW COULD GRADUALLY
ACQUIRE SUBTROPICAL CHARACTERISTICS OVER THE NEXT COUPLE OF DAYS.
THIS SYSTEM HAS A MEDIUM CHANCE...30 PERCENT...OF BECOMING A
SUBTROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT DRIFTS SLOWLY
WESTWARD TODAY AND NORTHWESTWARD ON TUESDAY. ADDITIONAL INFORMATION
ON THIS GALE AREA CAN BE FOUND IN HIGH SEAS FORECASTS ISSUED BY THE
NOAA NATIONAL WEATHER SERVICE UNDER AWIPS HEADER NFDHSFAT1...AND
UNDER WMO HEADER FZNT01 KWBC.

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

$$
FORECASTER STEWART

[ROLLTIDE]

40%

Return to Atlantic Graphical TWO
1. A NON-TROPICAL LOW PRESSURE SYSTEM LOCATED ABOUT 400 MILES SOUTHWEST OF BERMUDA IS PRODUCING GALE FORCE WINDS OVER AN AREA EXTENDING SEVERAL HUNDRED MILES TO THE NORTH OF THE CENTER. THE ASSOCIATED SHOWERS AND THUNDERSTORMS HAVE BECOME A LITTLE BETTER ORGANIZED OVERNIGHT...AND THE LOW COULD ACQUIRE SUBTROPICAL CHARACTERISTICS OVER THE NEXT DAY OR TWO. THIS SYSTEM HAS A MEDIUM CHANCE...40 PERCENT...OF BECOMING A SUBTROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES SLOWLY WESTWARD TODAY AND NORTHWESTWARD ON TUESDAY. ADDITIONAL INFORMATION ON THIS GALE AREA CAN BE FOUND IN HIGH SEAS FORECASTS ISSUED BY THE NOAA NATIONAL WEATHER SERVICE UNDER AWIPS HEADER NFDHSFAT1...AND UNDER WMO HEADER FZNT01 KWBC.

[dkmac]

[dkmac]

[dkmac]

JM

[h=1]Subtropical storm brewing near Bermuda; earthquakes and tornadoes for Oklahoma[/h]By Dr. Jeff Masters

Published: 7:52 AM CST on November 07, 2011
An extratropical low pressure system that moved off the coast of South Carolina over the weekend is camped out over the Atlantic about 400 miles southwest of Bermuda. Satellite loops reveal that this low (98L) has developed a respectable amount of heavy thunderstorm activity near its center, and in a curved band to the north. Bermuda radar shows weak rain bands from 98L rippling across the island, with the strongest rain showers well to the island's southwest. Sustained winds at the Bermuda airport reached 30 mph, gusting to 44 mph this morning. Sustained winds near tropical storm force were occurring this morning at buoy 41048, about 300 miles west of Bermuda. Wind at the buoy were 38 mph, gusting to 47 mph at 6:50 am EST. Strong upper-level winds out of the west are creating 35 - 45 knots of wind shear over 98L, limiting development. Ocean temperatures are near 26.5°C (80°F), which is right at the boundary of being warm enough to support tropical storm formation. Since 98L is getting its start as an extratropical storm, it has cold air at its core aloft, and is surrounded by a large amount of dry air to its south and west. This dry air and wind shear suggests that 98L will initially be Subtropical Storm Sean if it develops, and not Tropical Storm Sean.


Figure 1. Morning satellite image of 98L.

Forecast for 98L
98L will drift slowly west or northwest today and Tuesday. The latest SHIPS model forecast predicts wind shear will fall to 20 - 30 knots on Tuesday, which should allow for some increased organization of 98L. The computer models show little or no development of 98L, with none of our reliable models predicting 98L will become a hurricane. NHC gave 98L a 40% chance of developing into a subtropical storm by Wednesday in their 7 am EST Tropical Weather Outlook. I'd put these odds higher, at 50%. Since 98L is probably already generating sustained winds in excess of 39 mph, it will likely be named immediately if it gains enough organization, and skip being classified as a subtropical depression. Bermuda is the only land area that need concern itself with 98L, as a trough of low pressure is expected to absorb 98L and lift it quickly to the northeast on Thursday. The center of 98L should remain more than 200 miles away from Bermuda during the week, but heavy rain squalls from the storm are likely to affect the island at times between now and Thursday. The remnants of 98L will likely bring heavy rain to Nova Scotia, Canada on Thursday night or Friday morning.

Jeff Masters

[ROLLTIDE]

..

4:00 AM EST Tue Nov 8
Location: 27.2°N 69.4°W
Max sustained: 45 mph
Moving: Stationary
Min pressure: 1002 mb

[dkmac]

11AM

**this is from WU Tropical Weather page, NHC website is 404 at this time**

Sean expected to become a tropical storm later today...




summary of 1100 am AST...1500 UTC...information-----------------------------------------------location...27.7n 69.4wabout 420 mi...675 km SW of Bermudamaximum sustained winds...45 mph...75 km/hpresent movement...N or 360 degrees at 2 mph...4 km/hminimum central pressure...1002 mb...29.59 inches



watches and warnings--------------------changes with this advisory...

none.

Summary of watches and warnings in effect...

a tropical storm watch is in effect for...* Bermuda

a tropical storm watch means that tropical storm conditions arepossible within the watch area...generally within 48 hours.

Interests in Bermuda should monitor products issued by the BermudaWeather Service.



Discussion and 48-hour outlook------------------------------at 1100 am AST...1500 UTC...the center of subtropical storm Sean waslocated near latitude 27.7 north...longitude 69.4 west. The storm ismoving toward the north near 2 mph...4 km/h. A slow motion towardthe west-northwest is expected to begin later today...with a turntoward the northwest forecast by Wednesday.

Maximum sustained winds are near 45 mph...75 km/h...with highergusts. Little change in strength is forecast during the next 48hours.

Winds of 40 mph extend outward up to 380 miles...610 km...primarilyto the north of the center.

Estimated minimum central pressure is 1002 mb...29.59 inches.



Hazards affecting land----------------------wind...tropical storm conditions are possible on Bermuda lateThursday.

Surf...swells generated by Sean are expected to affect portions ofthe southeastern coast of the United States during the next coupleof days. These swells will cause life-threatening surf and ripcurrents. Please see statements from your local National WeatherService office for more details.



Next advisory-------------next intermediate advisory...200 PM AST.Next complete advisory...500 PM AST.

$$Forecaster Blake

[dkmac]

JM

[h=1]Sean, rare Mediterranean hybrid, and AK superstorm forms; quakes and tornadoes in OK[/h]By Dr. Jeff Masters

Published: 9:52 AM CST on November 08, 2011
Subtropical Storm Sean formed this morning between Bermuda and the Bahamas. Sean's formation brings this year's tally of named storms to eighteen, tying 2011 with 1969 as the 6th busiest Atlantic hurricane season since record keeping began in 1851. Only 2005, 1933, 1995, 1887, and 2010 have had more named storms. However, 2011 has had an unusually low percentage of its named storms reach hurricane strength. We've had an average number of hurricanes--six--meaning that only 33% of this year's named storms have made it to hurricane strength. Normally, 55 - 60% of all named storms intensify to hurricane strength in the Atlantic. There have been three major hurricanes in 2011, which is one above average, and the total Accumulated Cyclone Energy (ACE)--a measure of the destructive potential of this season's storms--has been about 20% above average. The rare combination of near-record ocean temperatures but unusually dry, stable air over the Atlantic is no doubt at least partially responsible for the unusually high count of named storms, but near-average number of hurricanes and ACE.


Figure 1. The subtropical disturbance that became Subtropical Storm Sean, as seen at 1 pm EST November 7, 2011. Image credit: NASA.

Infrared satellite loops reveal that Sean has developed a respectable amount of heavy thunderstorm activity near its center that is increasing in intensity and areal coverage. While the low-level circulation center is exposed to view, a band of thunderstorms is trying to wrap around and close of the center. If this occurs, more substantial strengthening can occur, since the center will be walled off from the dry air that is currently interfering with development. Bermuda radar shows weak rain bands from Sean rippling across the island, with the strongest rain showers well to the island's southwest. Sustained winds at the Bermuda airport have been under 30 mph this morning. Sustained winds near tropical storm force were occurring this morning at buoy 41048, about 300 miles west of Bermuda. Winds at the buoy were 38 mph, gusting to 47 mph at 6:50 am EST. Strong upper-level winds out of the west are creating about 20 knots of wind shear over Sean, which is low enough to allow some slow development. Sean is a relatively shallow storm, and the tops of its thunderstorms extend up only to about the 300 mb level. Normally, a tropical storm extends up to about 200 mb. The shallow nature of Sean's thunderstorms mean that the storm is less vulnerable to wind shear than normal, since the storm is not feeling the strongest winds aloft. Ocean temperatures are near 26.5°C (80°F), which is right at the boundary of being warm enough to support tropical storm formation.

Forecast for Sean
Sean will drift slowly west or northwest today and Wednesday. The latest SHIPS model forecast predicts wind shear will remain about where it is now through Thursday morning, which should allow Sean to slowly intensify to a 50 mph storm. If Sean can make the transition to a fully tropical storm, more significant intensification can occur. The computer models show little or no development of Sean, with none of our reliable models predicting it will become a hurricane. Bermuda is the only land area that need concern itself with Sean, as a trough of low pressure is expected to absorb the storm on Thursday and lift it quickly to the north or northeast. The center of Sean could pass close enough to Bermuda to bring the island heavy rain squalls and sustained winds of 40 - 45 mph on Thursday and Friday. NHC is giving a 28% chance that Bermuda will receive tropical storm-force winds of 39 mph. High wind shear should destroy Sean on Friday.


Figure 2. MODIS image of the hybrid low named "Rolf" in the Mediterranean Sea at 10:30 UTC November 8, 2011. Image credit: NASA.

Unusual tropical storm-like low forms off coast of France
An unusual hybrid low pressure system has formed in the Mediterranean Sea, about 100 miles south of the coast of France. The low began as an extratropical storm named "Rolf", but has stalled out over the relatively warm waters of the Mediterranean over the past two days, and has acquired tropical characteristics. Heavy thunderstorms have built over the northeast portion of the low, and the storm has a symmetric spiral shape with a cloud-free center, like a tropical storm. The Navy is calling this system Invest 99L. The National Hurricane Center is not responsible for the Mediterranean Sea, so they are not issuing any products for 99L. NOAA's Satellite and Information Service (NESDIS) is giving 99L a tropical classification based on its satellite presentation, with winds in the 40 - 45 mph range. French radar shows heavy rains from 99L are beginning to affect Southeast France and the island of Corsica. The Lion Buoy, located about 100 miles to the west of the center of 99L, recorded sustained winds of tropical storm force, 40 mph, at 00 UTC yesterday. Water temperatures at the buoy were 17°C (63°F), far below the 26°C threshold usually needed to sustain a tropical storm. The coldest waters I've seen a tropical storm form in were 22°C during Hurricane Epsilon of 2005. I doubt that NHC would name this system if they did have responsibility for the Mediterranean, due to the cold water temperatures.

"Rolf" is expected to move slowly northwards into the coast of South France by Wednesday night. Meteo France is predicting heavy rains of 30 - 40 mm/hr (1.2 - 1.6"/hr) will affect the coast Tuesday night through Wednesday, with sustained winds of 50 mph, gusting to 75 mph.


Figure 3. Hybrid subtropical storm of October 8, 1996, off the coast of Italy. According to Reale and Atlas (2001), the storm had characteristics similar to a hurricane, but formed over water of 21.5°C. "The maximum damage due to wind occurred over the Aeolian Islands, at 38.5°N, 15°E, to the northeast of Sicily: assistance for disaster relief was required. Unfortunately, no weather station data were available, but the media reported sheds, roofs and harbor devices destroyed, and houses and electric lines damaged, due to "extremely strong westerly wind." The perfect agreement between the observations at Ustica, the storm scale, the eye-like feature position and the damages over the Aeolian Island reasonably suggest that the hurricane-level intensity of 32 m/s (72 mph) was reached over the Aeolian Islands." A similar hybrid low affected Algeria on 9 - 10 November 2001. This storm produced upwards of 270 mm (10.6") of rain, winds of 33 m/s (74 mph), and killed 737 people near Algeirs, mostly from flooding and mud slides. Image credit: Dundee satellite receiving station.

According to research published by Gaertner et al. (2007), an increase in ocean temperatures of 3°C in the Mediterranean by the end of the century could lead to hurricanes forming there. Miguel Angel Gaertner of the University of Castilla-La Mancha in Toledo, Spain, ran 9 different climate models with resolutions of about 50 km and found that some (but not all) of the models simulated hurricanes in the Mediterranean in September by the end of the century, when ocean temperature could reach 30°C.

Though the Mediterranean may start seeing hurricanes by the end of the century, these storms should be rare and relatively short-lived for three reasons:

1) The Mediterranean is quite far north and is subject to strong wind shear from jet stream activity.

2) The waters are shallow, and have relatively low heat content. There is no deep warm water current like the Gulf Stream.

3) The Mediterranean has a lot of large islands and peninsulas poking into it, increasing the chances that a tropical storm would weaken when it encountered land.

References
Meteo France has an interesting animation of the predicted winds and temperatures over the next few days.

Gaertner, M. A., D. Jacob, V. Gil, M. Dominguez, E. Padorno, E. Sanchez, and M. Castro (2007), Tropical cyclones over the Mediterranean Sea in climate change simulations,, Geophys. Res. Lett., 34, L14711, doi:10.1029/2007GL029977.

Reale, O., and R. Atlas. 2001: Tropical Cyclone-Like Vortices in the Extratropics: Observational Evidence and Synoptic Analysis, Weather and Forecasting, 16, No. 1, pp. 7-34.


Figure 4. Radar reflectivity image from the Tipton, OK tornado of November 7, 2011, showing a classic hook echo.


Video 1. Reed Timmer video of the November 7, 2011 tornado in Tipton, OK. Here's another excellent video of the Tipton tornado and a tornado near Manitou, OK from Texas Storm Chasers. Storm chasing IS dangerous: one storm chaser had his vehicle overturned, but got into another vehicle and continued the chase.

Shaken and stirred: an earthquake and tornado for Oklahoma
It was a rare multi-natural hazard day for Oklahoma yesterday, as the state experienced both a tornado and an earthquake, six hours apart. The damaging magnitude 5.6 earthquake that shook the state Saturday night spawned a magnitude 4.7 aftershock at 8:46 pm CST yesterday, 44 miles east of Oklahoma City. And at 2:47 pm CST, a tornado touched down in Southwest Oklahoma near Tillman. The tornado destroyed an Oklahoma State University agricultural office, and damaged a hay barn at a dairy farm. No injuries were reported. The UK MailOnline has an interesting article showing the radar image from Saturday's quake, which captured a massive groups of birds and insects that took flight after the ground shook.

This afternoon, NOAA's Storm Prediction Center has placed Southeast Oklahoma, East Texas, Southeast Missouri, and most of Arkansas in its "Slight Risk" area for severe weather, thanks to a strong low pressure system moving across the Plains. During the late afternoon, severe thunderstorms with high winds and large hail and expected over the region, and we cannot rule out an isolated tornado.

Bering Sea superstorm targets Alaska
A massive blizzard the National Weather Service is calling one of the most severe Bering Sea storms on record is gathering strength today to the west of Alaska. The storm is expected to "bomb" to a central pressure of 945 - 950 mb Tuesday night, and to 940 mb on Wednesday. These pressures, characteristic of a Category 3 hurricane, will be strong enough to generate sustained winds of Category 1 hurricane force over the waters to the west of Alaska, with winds of 50 - 70 mph expected along portions of the coast. Nome, Alaska is expecting a storm surge of 8 - 10 feet. Waves of 15 - 25 feet with ice on top will batter the shores, causing severe damage to the coast.

Jeff Masters

[ROLLTIDE]

2PM

...Sean transitions to a tropical storm...

summary of 200 PM AST...1800 UTC...information ---------------------------------------------- location...27.7n 69.5w about 425 mi...685 km SW of Bermuda maximum sustained winds...45 mph...75 km/h present movement...stationary minimum central pressure...1002 mb...29.59 inches

[dkmac]

7AM

TROPICAL STORM SEAN INTERMEDIATE ADVISORY NUMBER 5A
NWS NATIONAL HURRICANE CENTER MIAMI FL AL192011
700 AM EST WED NOV 09 2011

...SEAN MEANDERING SOUTHWEST OF BERMUDA...


SUMMARY OF 700 AM EST...1200 UTC...INFORMATION
----------------------------------------------
LOCATION...27.8N 70.5W
ABOUT 470 MI...755 KM SW OF BERMUDA
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...W OR 270 DEGREES AT 3 MPH...6 KM/H
MINIMUM CENTRAL PRESSURE...995 MB...29.38 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* BERMUDA

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA WITHIN 36 HOURS.

INTERESTS IN BERMUDA SHOULD MONITOR PRODUCTS ISSUED BY THE BERMUDA
WEATHER SERVICE.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 700 AM EST...1200 UTC...THE CENTER OF TROPICAL STORM SEAN WAS
LOCATED NEAR LATITUDE 27.8 NORTH...LONGITUDE 70.5 WEST. SEAN IS
MOVING TOWARD THE WEST NEAR 3 MPH...6 KM/H. A GRADUAL TURN TOWARD
THE NORTH IS EXPECTED OVER THE NEXT 24 HOURS...FOLLOWED BY A TURN
TOWARD THE NORTHEAST AND AN INCREASE IN FORWARD SPEED ON THURSDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 50 MPH...85 KM/H...WITH HIGHER
GUSTS. SOME STRENGTHENING IS POSSIBLE TODAY AND TONIGHT.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 290 MILES...465 KM
FROM THE CENTER. NOAA BUOY 41047 RECENTLY REPORTED A 1-MINUTE MEAN
WIND OF 40 MPH...65 KM/H...AND A WIND GUST OF 45 MPH...72 KM/H.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 995 MB...29.38 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE EXPECTED ON BERMUDA BY THURSDAY
AFTERNOON OR THURSDAY NIGHT.

SURF...SWELLS GENERATED BY SEAN ARE EXPECTED TO AFFECT PORTIONS OF
THE SOUTHEASTERN COAST OF THE UNITED STATES AND BERMUDA DURING THE
NEXT COUPLE OF DAYS...CAUSING LIFE-THREATENING SURF AND RIP
CURRENTS. PLEASE SEE STATEMENTS FROM YOUR LOCAL NATIONAL WEATHER
SERVICE OFFICE FOR MORE DETAILS.


NEXT ADVISORY
-------------
NEXT COMPLETE ADVISORY...1000 AM EST.

$$
FORECASTER BEVEN

TROPICAL STORM SEAN DISCUSSION NUMBER 5
NWS NATIONAL HURRICANE CENTER MIAMI FL AL192011
400 AM EST WED NOV 09 2011

SEAN HAS AGAIN CHANGED LITTLE IN STRUCTURE DURING THE PAST SEVERAL
HOURS. A CENTRAL CONVECTIVE BAND IS PRESENT WITHIN 60-75 N MI OF
THE CENTER...MAINLY IN THE SOUTHEASTERN SEMICIRCLE...WHILE OUTER
CONVECTIVE BANDS ARE PRESENT UP TO 240 N MI FROM THE CENTER IN THE
NORTHEASTERN SEMICIRCLE. SATELLITE INTENSITY ESTIMATES FROM SAB
AND TAFB ARE 45 KT...AND THAT REMAINS THE INITIAL INTENSITY FOR
THIS ADVISORY. THE CENTRAL PRESSURE HAS BEEN ADJUSTED DOWNWARD
BASED ON OBSERVATIONS FROM NOAA BUOY 41047.

THE INITIAL MOTION REMAINS 270/3. SEAN IS EMBEDDED IN A DEEP-LAYER
CYCLONIC CIRCULATION THAT IS CUT OFF FROM THE WESTERLIES SOUTH OF A
RIDGE OVER THE NORTHWESTERN ATLANTIC. A STRONG MID/UPPER-LEVEL
TROUGH AND ASSOCIATED SURFACE COLD FRONT ARE MOVING EASTWARD
THROUGH THE MISSISSIPPI VALLEY...AND THE DYNAMICAL MODELS FORECAST
THIS SYSTEM TO REACH THE WESTERN ATLANTIC IN ABOUT 36 HOURS. THIS
EVOLUTION SHOULD CAUSE SEAN TO TURN NORTHWARD DURING THE NEXT
24 HOURS...AND THEN TURN NORTHEASTWARD IN DEEP-LAYER SOUTHWESTERLY
FLOW AHEAD OF THE APPROACHING TROUGH. WHILE THE DYNAMICAL MODELS
AGREE ON THIS SCENARIO...THERE IS SOME SPREAD IN BOTH THE DIRECTION
AND SPEED OF FORWARD MOTION AFTER 24 HOURS. THE ECMWF MODEL IS ON
THE RIGHT SIDE OF THE GUIDANCE ENVELOPE AND TAKES THE CENTER NEAR
BERMUDA...WHILE THE GFDL AND UKMET ARE ON THE LEFT SIDE FORECASTING
A TRACK CLOSER TO NOVA SCOTIA AND NEWFOUNDLAND. THE GUIDANCE
ENVELOPE HAS SHIFTED TO THE LEFT/NORTH COMPARED TO 6 HOURS AGO...
AND THE NEW FORECAST TRACK IS ALSO SHIFTED IN THAT DIRECTION.
HOWEVER...OUT OF RESPECT FOR THE ECMWF AND THE PREVIOUS FORECAST
THE NEW FORECAST TRACK LIES TO THE RIGHT OF THE CENTER OF THE
GUIDANCE ENVELOPE AND THE CONSENSUS MODELS.

SEAN IS IN A REGION OF LIGHT/MODERATE VERTICAL WIND SHEAR NEAR THE
CENTER OF THE CUT-OFF LOW. THE DYNAMICAL MODELS SUGGEST THE
PRESENT SHEAR SHOULD CONTINUE FOR THE NEXT 12-24 HOURS...FOLLOWED
BY A SIGNIFICANT INCREASE IN SHEAR CAUSED BY THE TROUGH APPROACHING
FROM THE WEST. THIS SHOULD ALLOW SEAN TO STRENGTHEN SOME TODAY...
FOLLOWED BY A WEAKENING TREND AFTER 24 HOURS. SEAN IS FORECAST TO
BECOME EXTRATROPICAL AS IT MERGES WITH THE APPROACHING COLD FRONT
BETWEEN 48-72 HOURS...WITH THE CIRCULATION BECOMING TOTALLY
ABSORBED BY THE FRONT BY 96 HOURS. THE NEW INTENSITY FORECAST IS
SIMILAR TO THE PREVIOUS FORECAST...WITH JUST A LITTLE LESS
STRENGTHENING DURING THE FIRST 24-36 HOURS. IT SHOULD BE NOTED
THAT MANY OF THE DYNAMICAL MODELS SHOW THE CIRCULATION OF SEAN
DISSIPATING BEFORE 72 HOURS...SO THE CURRENT FORECAST LIFETIME
COULD BE GENEROUS.


FORECAST POSITIONS AND MAX WINDS

INIT 09/0900Z 27.9N 70.4W 45 KT 50 MPH
12H 09/1800Z 28.4N 70.7W 50 KT 60 MPH
24H 10/0600Z 29.4N 70.7W 50 KT 60 MPH
36H 10/1800Z 30.6N 69.7W 50 KT 60 MPH
48H 11/0600Z 33.1N 67.4W 45 KT 50 MPH
72H 12/0600Z 38.5N 59.0W 45 KT 50 MPH...POST-TROP/EXTRATROP
96H 13/0600Z...DISSIPATED

$$
FORECASTER BEVEN

[dkmac]

4AM: Sean may reach hurricane strength in the next 24 hours.

TROPICAL STORM SEAN DISCUSSION NUMBER 9
NWS NATIONAL HURRICANE CENTER MIAMI FL AL192011
400 AM EST THU NOV 10 2011

INFRARED AND MICROWAVE SATELLITE IMAGERY THIS MORNING SHOWS THAT
SEAN IS SLOWLY BECOMING BETTER ORGANIZED...WITH INCREASING
CONVECTIVE BANDING AROUND THE CENTER AND OCCASIONAL ATTEMPTS AT EYE
FORMATION. SATELLITE INTENSITY ESTIMATES FROM SAB AND TAFB ARE 55
KT...AND THAT REMAINS THE INITIAL INTENSITY. THE CYCLONE CURRENTLY
HAS GOOD CIRRUS OUTFLOW IN THE NORTH SEMICIRCLE.

SEAN CONTINUES ITS NORTHERLY TRACK WITH AN INITIAL MOTION OF 355/7.
WATER VAPOR IMAGERY SHOWS SOUTHWESTERLY MID/UPPER-LEVEL FLOW
ASSOCIATED WITH A TROUGH OVER THE EASTERN UNITED STATES APPROACHING
THE CYCLONE...AND THE GUIDANCE IS IN GOOD AGREEMENT THAT THIS
SHOULD CAUSE SEAN TO TURN NORTHEASTWARD IN THE NEXT 12 HOURS.
AFTER THAT...THE CYCLONE SHOULD ACCELERATE NORTHEASTWARD DURING THE
REMAINDER OF ITS LIFETIME. THE NEW FORECAST TRACK FOLLOWS THIS
SCENARIO AND IS SIMILAR TO...BUT NORTH OF...THE PREVIOUS TRACK.
THE FORECAST TRACK IS NEAR THE CENTER OF THE TRACK GUIDANCE
ENVELOPE.

THERE IS PERHAPS 12-24 HOURS FOR SEAN TO STRENGTHEN BEFORE STRONG
VERTICAL WIND SHEAR IMPACTS THE STORM. GIVEN THE CURRENT
STRUCTURE...THE INTENSITY FORECAST CALLS FOR SEAN TO REACH HURRICANE
STRENGTH IN 24 HOURS IN AGREEMENT WITH THE PREVIOUS FORECAST.
AFTER THAT...STRONG SHEAR AND THE START OF EXTRATROPICAL TRANSITION
SHOULD CAUSE WEAKENING. EXTRATROPICAL TRANSITION IS EXPECTED TO BE
COMPLETE BY 48 HOURS...AND BY 72 HOURS SEAN IS EXPECTED TO BE
ABSORBED BY A LARGER BAROCLINIC SYSTEM TO ITS NORTH. AS NOTED IN
THE PREVIOUS DISCUSSION...IT IS POSSIBLE THAT SEAN COULD DISSIPATE
EARLIER THAN CURRENTLY FORECAST.

FORECAST POSITIONS AND MAX WINDS

INIT 10/0900Z 30.2N 70.9W 55 KT 65 MPH
12H 10/1800Z 31.2N 69.8W 60 KT 70 MPH
24H 11/0600Z 33.4N 67.2W 65 KT 75 MPH
36H 11/1800Z 37.0N 63.0W 55 KT 65 MPH
48H 12/0600Z 41.5N 56.5W 45 KT 50 MPH...POST-TROP/EXTRATROP
72H 13/0600Z...ABSORBED BY EXTRATROPICAL LOW

$$
FORECASTER BEVEN