Tropical weather analysis - October 28, 2012

By: KoritheMan , 6:44 AM GMT on October 29, 2012

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Sandy

Hurricane Sandy continues to pose a serious threat to the mid-Atlantic and New England coasts, and it is likely to be a historical storm for that region. As of the latest NHC advisory, the following information was posted on the storm:

Wind: 75 mph, with higher gusts
Location: 35.2°N 70.5°W
Movement: N at 14 mph
Pressure: 950 mb
Category: 1 (Saffir-Simpson Hurricane Scale)

Satellite images suggest that Sandy is better organized compared to 24 hours, and a fortuitous 0158 UTC SSMI microwave pass suggested the reformation of an inner core. Indeed, earlier aircraft reports on Sunday suggested that fragments of an eyewall were beginning to build. Although the earlier eye feature has disappeared in conventional satellite pictures, a band of relatively deep convection envelopes all but the eastern portion of the circulation center.



Figure 1. Latest infrared satellite image of Hurricane Sandy. Image credit: NOAA

High cloud motions suggest that the vertical shear over the hurricane has decreased, and I see very little evidence of large-scale wind shear at this point. Given that Sandy is still over decently warm waters, and since she has been able to mix out most of the dry air that had been slamming her, there is a slight chance of some tropical intensification over the next 12 hours or so. It should be noted that flight-level winds reported by the air force reconnaissance aircraft over the last 12 hours have been over 100 knots at times, which suggests that Sandy still has a vigorous circulation, and it would probably not take much convection to bring some of these winds down to the surface. Since the environment appears generally favorable, especially for this time of year, I will forecast some slight reintensification, which will probably occur during the diurnal convective maximum period that will emerge in a few hours. This will probably result in a somewhat stronger system for New England as the hurricane subsequently deepens through baroclinic processes.

There is little change to the intensity forecast philosophy, but again, I want to emphasize that Sandy could come in with winds at around 75 kt if it actually does strengthen through tropical processes this morning. Regardless, Sandy is expected to reintensify a little as it interacts with the negatively tilted upper trough moving through far northern New England and southern Canada. Indeed, surface observations over the Ohio Valley and the upper portion of the Appalachian Mountains suggest that surface temperatures are rather cold, and areal dew points rather meager. This suggests that a highly baroclinic environment awaits our hurricane, which should lead to an abrupt transition from tropical to extratropical prior to or just after landfall. I will continue to show the system hanging on, albeit barely, to tropical cyclone status at US landfall. However, Sandy will not be a typical hurricane, and it is still possible that the cyclone will lose tropical characteristics prior to moving inland. Sandy is forecast to weaken rapidly after landfall.

Coastal and offshore observations suggest that sustained tropical storm force winds are still occurring over sections of the North Carolina Outer Banks and adjacent Atlantic waters, and tropical storm warnings are still in effect for this area. A tropical storm warning is also in effect for Bermuda, and Saint David's has reported tropical storm force wind gusts for the last three days. These winds should gradually subside as Sandy steadily approaches the United States.

Sandy continues to pose a significant hazard for the mid-Atlantic and New England; indeed, the hazards appear so extensive that it is impossible to list the specifics of all of them. Significant coastal flooding, especially if Sandy hits near the time of high tide, can be expected to occur. In this case, Sandy's associated wind field is so enormous the typical "near and to the north of the center" rule commonly applied to more classical hurricanes doesn't quite apply. Water level rises can be expected hundreds of miles north of where the center comes ashore. A cursory glance at tide gauges across the northeastern United States suggests that water level rises are already occurring well in advance of the center. In addition to coastal flooding, the large circulation of Sandy is expected to produce a prolonged fetch of sustained tropical storm force winds over much of the mid-Atlantic and New England, along with hurricane force winds near the coast, especially southwest of the center where those winds have consistently been reported. Heavy rainfall/inland flooding will also be an issue, although I suspect that the rainfall with Sandy will be a little less than that of Hurricane Irene last year due to the more baroclinic environment. While tornadoes would ordinarily accompany a landfalling tropical cyclone, upper air data show a rather marginal thermodynamic environment, largely due to the cold airmass associated with the aforementioned trough. That said, a conditional threat for damaging winds, perhaps to hurricane force, in brief convective downdrafts will be possible as dewpoint depressions remain rather large. This potential will diminish with northward extent. Heavy mountain snowfall will also be possible across the southern portion of the Appalachian Mountains, possibly up to about 18 inches in higher elevations. For storm information specific to your area, please monitor advisory products issued by your local National Weather Service.

As alluded to yesterday, the National Hurricane Center has decided to forgo conventional hurricane watches and warnings since Sandy is likely to become post-tropical rather quickly after landfall. However, this does not mitigate the threat, and Sandy has the potential to cause damage equivalent to that of a major hurricane. Residents living in the affected areas should prepare now while they have a chance, and they should take this storm very seriously. If you have a chance to get out, do so. Do not wait until the last minute to decide to leave. At that point, conditions will have become too hazardous.

Sandy appears to have made the anticipated northward turn based on satellite images. 0z upper air data and water vapor imagery show a substantial mid-level ridge exists over Bermuda and Atlantic Canada, while the large-scale trough over the Great Lakes region is gradually lifting northward into southern Canada. However, abundant southerly flow remains along the southern extent of this trough, which should act in tandem with the ridge to nudge Sandy inland in about 24 hours. The models have in general been trending toward a faster landfall, and my forecast is nudged in that direction. However, the landfall point remains essentially unchanged, with a landfall in southern New Jersey around 2 AM Tuesday morning eastern time. This forecast will place Long Island in a prolonged fetch of onshore winds, for up to more than 24 hours. This could pose a particularly hazardous situation for New York City, which escaped the full wrath of Hurricane Irene last year. I feel there's a decent chance of the subway system in that city being flooded, perhaps as high as 60%. After landfall, Sandy is forecast to get ejected toward the north and east as it moves closer to the base of the Canadian upper trough.

5-day intensity forecast

INITIAL 10/29 0600Z 65 KT 75 MPH
12 hour 10/29 1800Z 70 KT 80 MPH
24 hour 10/30 0600Z 75 KT 85 MPH...ON THE COAST
36 hour 10/30 1800Z 65 KT 75 MPH...INLAND POST-TROPICAL/EXTRATROPICAL
48 hour 10/31 0600Z 50 KT 60 MPH...POST-TROPICAL/EXTRATROPICAL
72 hour 11/01 0600Z 30 KT 35 MPH...POST-TROPICAL/EXTRATROPICAL
96 hour 11/02 0600Z 25 KT 30 MPH...POST-TROPICAL/EXTRATROPICAL
120 hour 11/03 0600Z 20 KT 25 MPH...POST-TROPICAL/EXTRATROPICAL

5-day track forecast



Figure 2. My 5-day forecast track for Sandy.

Watches and warnings

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* NORTH OF SURF CITY TO DUCK NORTH CAROLINA
* PAMLICO AND ALBEMARLE SOUNDS
* BERMUDA

IN ADDITION...HURRICANE-FORCE WINDS ARE EXPECTED ALONG PORTIONS OF
THE COAST BETWEEN CHINCOTEAGUE VIRGINIA AND CHATHAM MASSACHUSETTS.
THIS INCLUDES THE TIDAL POTOMAC FROM COBB ISLAND TO SMITH POINT...
THE MIDDLE AND UPPER CHESAPEAKE BAY...DELAWARE BAY...AND THE COASTS
OF THE NORTHERN DELMARVA PENINSULA...NEW JERSEY...THE NEW YORK CITY
AREA...LONG ISLAND...CONNECTICUT...AND RHODE ISLAND.

TROPICAL-STORM-FORCE WINDS ARE EXPECTED NORTH OF CHATHAM TO
MERRIMACK RIVER MASSACHUSETTS...THE LOWER CHESAPEAKE BAY...AND
SOUTH OF CHINCOTEAGUE TO DUCK NORTH CAROLINA...THE NORTHERN
ENDPOINT OF THE TROPICAL STORM WARNING.

OTHER COASTAL AND INLAND WATCHES AND WARNINGS ARE IN EFFECT FOR
THESE AREAS. PLEASE SEE STATEMENTS FROM LOCAL NATIONAL WEATHER
SERVICE FORECAST OFFICES.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA IN THE UNITED
STATES...INCLUDING POSSIBLE INLAND WATCHES AND WARNINGS...PLEASE
MONITOR PRODUCTS ISSUED BY YOUR LOCAL NATIONAL WEATHER SERVICE
FORECAST OFFICE. FOR STORM INFORMATION SPECIFIC TO YOUR AREA OUTSIDE
THE UNITED STATES...PLEASE MONITOR PRODUCTS ISSUED BY YOUR NATIONAL
METEOROLOGICAL SERVICE.

Land hazards

HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS...OR GALE FORCE WINDS...ARE ALREADY
OCCURRING OVER COASTAL NORTH CAROLINA...SOUTHEASTERN VIRGINIA...THE
DELMARVA PENINSULA AND COASTAL NEW JERSEY. GALE FORCE WINDS ARE
EXPECTED TO ARRIVE ALONG OTHER PORTIONS OF THE MID-ATLANTIC
COAST...LONG ISLAND...AND SOUTHERN NEW ENGLAND...LATER THIS
MORNING. WINDS OF HURRICANE FORCE COULD REACH THE MID-ATLANTIC
STATES...INCLUDING LONG ISLAND...LATER TODAY. WINDS AFFECTING THE
UPPER FLOORS OF HIGH-RISE BUILDINGS WILL BE SIGNIFICANTLY STRONGER
THAN THOSE NEAR GROUND LEVEL.

STORM SURGE...THE COMBINATION OF AN EXTREMELY DANGEROUS STORM SURGE
AND THE TIDE WILL CAUSE NORMALLY DRY AREAS NEAR THE COAST TO BE
FLOODED BY RISING WATERS. THE WATER COULD REACH THE FOLLOWING
DEPTHS ABOVE GROUND IF THE PEAK SURGE OCCURS AT THE TIME OF HIGH
TIDE...

NC NORTH OF SURF CITY INCLUDING PAMLICO/ALBEMARLE SOUNDS...4 TO 6 FT
SE VA AND DELMARVA INCLUDING LOWER CHESAPEAKE BAY...2 TO 4 FT
UPPER AND MIDDLE CHESAPEAKE BAY...1 TO 3 FT
LONG ISLAND SOUND...RARITAN BAY...AND NEW YORK HARBOR...6 TO 11 FT
ELSEWHERE FROM OCEAN CITY MD TO THE CT/RI BORDER...4 TO 8 FT
CT/RI BORDER TO THE SOUTH SHORE OF CAPE COD INCLUDING BUZZARDS
BAY AND NARRAGANSETT BAY...3 TO 6 FT
CAPE COD TO THE MA/NH BORDER INCLUDING CAPE COD BAY...2 TO 4 FT
MA/NH BORDER TO THE U. S./CANADA BORDER...1 TO 3 FT

SURGE-RELATED FLOODING DEPENDS ON THE RELATIVE TIMING OF THE SURGE
AND THE TIDAL CYCLE...AND CAN VARY GREATLY OVER SHORT DISTANCES.
GIVEN THE LARGE WIND FIELD ASSOCIATED WITH SANDY...ELEVATED WATER
LEVELS COULD SPAN MULTIPLE TIDE CYCLES RESULTING IN REPEATED AND
EXTENDED PERIODS OF COASTAL AND BAYSIDE FLOODING. IN ADDITION...
ELEVATED WATERS COULD OCCUR FAR REMOVED FROM THE CENTER OF SANDY.
FURTHERMORE...THESE CONDITIONS WILL OCCUR REGARDLESS OF WHETHER
SANDY IS A TROPICAL OR POST-TROPICAL CYCLONE. FOR INFORMATION
SPECIFIC TO YOUR AREA...PLEASE SEE PRODUCTS ISSUED BY YOUR LOCAL
NATIONAL WEATHER SERVICE OFFICE.

RAINFALL...RAINFALL TOTALS OF 3 TO 6 INCHES ARE EXPECTED OVER FAR
NORTHEASTERN NORTH CAROLINA WITH ISOLATED MAXIMUM TOTALS OF 8
INCHES POSSIBLE. RAINFALL AMOUNTS OF 4 TO 8 INCHES ARE EXPECTED
OVER PORTIONS OF THE MID ATLANTIC STATES...INCLUDING THE DELMARVA
PENINSULA...WITH ISOLATED MAXIMUM AMOUNTS OF 12 INCHES POSSIBLE.
RAINFALL AMOUNTS OF 1 TO 3 INCHES WITH ISOLATED MAXIMUM AMOUNTS
OF 5 INCHES ARE POSSIBLE FROM THE SOUTHERN TIER OF NEW YORK STATE
NORTHEASTWARD THROUGH NEW ENGLAND.

SNOWFALL...SNOW ACCUMULATIONS OF 2 TO 3 FEET ARE EXPECTED IN THE
MOUNTAINS OF WEST VIRGINIA...WITH LOCALLY HIGHER TOTALS TONIGHT
THROUGH TUESDAY NIGHT. SNOWFALL OF 1 TO 2 FEET IS EXPECTED IN
THE MOUNTAINS OF SOUTHWESTERN VIRGINIA TO THE KENTUCKY BORDER...
WITH 12 TO 18 INCHES OF SNOW POSSIBLE IN THE MOUNTAINS NEAR THE
NORTH CAROLINA/TENNESSEE BORDER AND IN THE MOUNTAINS OF WESTERN
MARYLAND.

SURF...DANGEROUS SURF CONDITIONS WILL CONTINUE FROM FLORIDA THROUGH
NEW ENGLAND FOR THE NEXT COUPLE OF DAYS.



Invest 98E

A weak area of low pressure located about 650 miles southwest of Manzanillo continues to produce disorganized showers and thunderstorms. Satellite and microwave fixes suggest that the low-level center is on the north side of the convection. A burst of thunderstorms has recently obscured all but the far northern fringes of the circulation, which suggests that the system is still hanging on.

The biggest impediment continues to be competition within a convectively active Intertropical Convergence Zone. Nevertheless, since the system appears better organized than yesterday, there is the potential for some development before upper-level winds become less favorable in about two or three days.

Probability of development in 48 hours: 50%

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4. WunderAlertBot (Admin)
5:57 AM GMT on October 31, 2012
KoritheMan has created a new entry.
3. Slamguitar
7:56 AM GMT on October 29, 2012
Thanks Kori! I see you went 10% higher than Jeff on the NYC subway flood potential, lol.
Member Since: July 2, 2011 Posts: 0 Comments: 1183
2. LostTomorrows
7:55 AM GMT on October 29, 2012
Thanks man,

Question: There are some that are saying that they have found surface winds of roughly 78 kt on their most recent pass - do you think that the NHC will go to 90 mph? I think that, if there are legitimate observations of surface winds at that level, that they shouldn't dare be conservative with a storm in her position. If it's 90 mph, it's 90 mph, and perhaps people will be like "Oh crap, she's getting stronger. Well, those who see hurricanes as only wind machines anyway.

Member Since: August 26, 2008 Posts: 0 Comments: 618
1. helmingstay
7:26 AM GMT on October 29, 2012
Nice summary, thanks!
Member Since: September 12, 2008 Posts: 0 Comments: 16

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About KoritheMan

I'm just a 23 year old with an ardent passion for weather. I first became aware of this interest after Tropical Storm Isidore struck my area in 2002.

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