KoritheMan's WunderBlog

Tropical weather analysis - October 31, 2012

By: KoritheMan, 5:57 AM GMT on October 31, 2012

Rosa

Tropical Storm Rosa formed early Tuesday over the eastern Pacific well away from land. As of the latest NHC advisory, the following information was available on the cyclone:

Wind: 45 mph, with higher gusts
Location: 14.5°N 117.0°W
Movement: W at 5 mph
Pressure: 1003 mb

There has been little change to Rosa since the advent of the latest NHC advisory. The central convection, while deep, has become a bit fragmented. In addition, the central dense overcast appears to have elongated some, while earlier microwave data suggested that the center was embedded in the western end of the cloud canopy, which suggests that some westerly shear is affecting Rosa.



Figure 1. Latest infrared satellite image of Tropical Storm Rosa. Image credit: NOAA

Environmental conditions have not yet become unfavorable enough to bar a little bit of additional strengthening, and that is shown in the forecast. It would not be surprising, however, if Rosa fails to strengthen before the shear increases. That is forecast to occur in about 24 hours. It should be noted that the tropical storm will remain over warm water throughout the forecast period as it remains south of the 26C isotherm, which will probably not result in a demise as abrupt as is usually the case for the Eastern Pacific storms in unfavorable environments. Dissipation is shown in about four days, but the system as a whole is expected to retain some identity as a remnant area of low pressure through the next five days.

In an interesting turn of events, the track forecast is actually more complicated than the intensity forecast. Rosa is currently south of a mid-level ridge which should steer the tropical cyclone its general westward course for the next day or so. Beyond that time, there is significant divergence in the model guidance, with the GFS taking Rosa northward, and the GFDL taking Rosa northeastward toward southern Baja. The remainder of the models, comprised of the reliable ECMWF, show Rosa turning west-southwestward as the ridge strengthens. Since the ambient 500 mb vorticity fields in the models look suspiciously the same, I am a little confused as to the reason for the discrepancy. Water vapor imagery shows an abundance of southwesterly flow to the north of Rosa, which suggests there is a weakness in the ridge. This appeared on earlier UW-CIMSS steering data as well. Upstream, however, one can clearly see large-scale westerly flow approaching those southwesterlies. The models suggest that the flow north of Rosa will become largely zonal as this flow pivots eastward; such a pattern usually heralds ridging.

The reason for the disagreement could be due to the GFS/GFDL showing a somewhat stronger Rosa, which seems a little unrealistic given current trends. Overall, the GFS has shifted southward since 18z. Suspecting that the surrounding environment is rather complex, and that the models are understandably having a difficult time resolving it, my forecast will lean toward the consensus, and the National Hurricane Center. I may be showing too much fast motion near the end of the period, but no need to be uber conservative with a storm well away from land. Revisions will be made as necessary. Confidence in this forecast is not especially high.

5-day intensity forecast

INITIAL 10/31 0600Z 40 KT 45 MPH
12 hour 10/31 1800Z 45 KT 50 MPH
24 hour 11/01 0600Z 40 KT 45 MPH
36 hour 11/01 1800Z 40 KT 45 MPH
48 hour 11/02 0600Z 35 KT 40 MPH
72 hour 11/03 0600Z 30 KT 35 MPH
96 hour 11/04 0600Z 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW
120 hour 11/05 0600Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW

5-day track forecast



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

2012 East Pacific hurricane season Tropical Storm Rosa

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Tropical weather analysis - October 28, 2012

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

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%

2012 Atlantic hurricane season 2012 East Pacific hurricane season Hurricane Sandy Invest 98E

Updated: 6:46 AM GMT on October 29, 2012

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Tropical weather analysis - October 28, 2012

By: KoritheMan, 7:23 AM GMT on October 28, 2012

Sandy

Hurricane Sandy continues moving toward across the western Atlantic. As of the latest NHC advisory, the following information was available on Sandy:

Wind: 75 mph, with higher gusts
Location: 31.5°N 73.7°W
Movement: NE at 14 mph
Pressure: 960 mb
Category: 1 (Saffir-Simpson Hurricane Scale)

After a burst of convection earlier this evening, the thunderstorm activity with Sandy has become a little thin. However, a fresh burst has recently occurred about 50 miles north of the center, which suggests that Sandy is still clinging to tropical cyclone status; an AMSU microwave pass near 2100 UTC also suggested that the cyclone still possessed a warm core.



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

Having said that, Sandy is certainly not a typical hurricane. It is interacting with a rather vigorous mid autumn cold front, with coastal radars suggesting that the heaviest rains are in a band well to the west of the center. In addition, water vapor imagery and various microwave data indicate that the hurricane remains embedded in a tongue of very dry air, which is at least partially responsible for the lack of deep convection within the eastern half of the storm. All of this suggests that Sandy is deriving at least a portion of its energy from baroclinic processes.

Interestingly, the vertical shear over Sandy appears to have decreased a little, which I admit was well forecast by the GFS. While this could argue for some restrengthening through tropical processes, sometimes it is better to use one's personal experience and intuition rather than blindly trust a computer model forecast. The environment around Sandy is at the bottom end of the tropical spectrum, with the western side actually more tropical than the eastern half due to that portion of the circulation being more embedded within the warm front associated with the eastern United States cold front. Indeed, the eastern side of the cyclone center appears to be pulling in the cold airmass over Florida and the Gulf Coast states in the wake of the trough. Further corroboration to this is given by areal dew point readings in the upper 50s to lower 60s across coastal sections of South and North Carolina.

My doubts notwithstanding, perhaps there is some truth to the GFS/SHIPS forecast of lower shear: as I said above, the mean vertical shear over the hurricane does appear to have decreased compared to 24 hours ago, and I think dry air is more the reason Sandy is not developing a core again than wind shear. Since there appears to be more baroclinicity than not, I am not forecasting any restrengthening as a tropical cyclone. However, it remains an outside possibility.

In about 24 hours, the global and dynamical models suggest that Sandy will enter a highly baroclinic environment characterized by strong southwesterly flow aloft, progressively cooler water, and cold air advection on the backside of the upper trough. These factors are anticipated to reinvigorate the cyclone a bit, and Sandy is forecast to be of hurricane strength when it makes landfall. Subsequent to moving inland, the storm is forecast to steadily weaken as it moves away from the core of baroclinic forcing. To maintain some continuity with the previous forecast, I still have Sandy as a tropical entity at landfall, although it will clearly not be a very typical one, if that verifies at all.

Coastal buoy observations suggest that Sandy is producing sustained winds to about 35 kt, minimal tropical storm force, across coastal sections of North Carolina. Duck, North Carolina, located in far eastern North Carolina right on the Outer Banks recently reported a sustained wind of 41 mph. Surface observations suggest that these winds have not really penetrated inland, although there have been several reports of tropical storm force wind gusts along the far outer fringes of Sandy's large circulation. These winds are slowly spreading spread northward as Sandy moves in tandem with the upper trough/cold front.

Due to the likelihood of Sandy losing tropical characteristics shortly before landfall, it was decided as a course of least regret by the National Hurricane Center not to issue hurricane watches or warnings north of the tropical storm warning, as the abrupt change in the status of the cyclone would result in an equally abrupt change in the watches and warnings. Instead, high wind watches and warnings have been issued in place of the hurricane bulletins. For forecasts specific to your area, please monitor forecasts issued by your local National Weather Service forecast office. I want to accentuate the threat Sandy poses, and that the status of the warnings are irrelevant. This will deliver significant impacts across virtually all of New England given the enormous wind field, which eclipses even that of Katrina and Ike. I cannot stress enough how seriously people need to take this storm. If things as verify as forecast, Sandy will be worse than Irene or Lee by far.

Widespread and prolonged power outages, possibly up to two weeks in some select locations, heavy rain/inland flooding, significant coastal flooding, and snowfall on the backside of the cyclone are likely across the affected areas. The snows could be particularly heavy over the mountains of West Virginia. Given the marginal thermodynamic environment/stable boundary layer, the attendant threat for tornadoes appear rather low at the moment.

The track forecast remains straightforward, as the model consensus remains tightly clustered. Sandy is accelerating toward the northeast as it moves along the deep-layer southwesterly flow associated with the eastern United States trough. This motion is forecast to continue for another 24 hours or so, after which time the hurricane is forecast to turn northward, northwestward, and finally west-northwestward in an unusual beeline for the New England coast. This occurs underneath a building mid-level ridge over Atlantic Canada as the trough lifts out to the northeast. The consensus has barely budged, and my forecast is only a little north of yesterday's, in best agreement with the TVCE consensus at 0z. This is along the left edge of the dynamical model suite.

Residents living in the affected areas should be making preparations now, as weather conditions will begin to go downhill as early as Sunday night. Landfall is expected Tuesday morning around 3 or 4 in the morning.

5-day intensity forecast

INITIAL 10/28 0600Z 65 KT 75 MPH
12 hour 10/28 1800Z 65 KT 75 MPH
24 hour 10/29 0600Z 65 KT 75 MPH
36 hour 10/29 1800Z 70 KT 80 MPH
48 hour 10/30 0600Z 70 KT 80 MPH...NEAR NEW ENGLAND
72 hour 10/31 0600Z 45 KT 50 MPH...INLAND POST-TROPICAL/EXTRATROPICAL
96 hour 11/01 0600Z 30 KT 35 MPH...POST-TROPICAL/EXTRATROPICAL
120 hour 11/02 0600Z 25 KT 30 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...
* SOUTH SANTEE RIVER SOUTH CAROLINA TO DUCK NORTH CAROLINA
* PAMLICO AND ALBEMARLE SOUNDS
* BERMUDA

IN ADDITION...HIGH WIND WATCHES AND WARNINGS...ALONG WITH
OTHER WATCHES AND WARNINGS...ARE IN EFFECT FOR THE MID-ATLANTIC
STATES AND MUCH OF NEW ENGLAND. 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.

Storm surge values

Here are the storm surge values for the affected areas as predicted by the National Hurricane Center.

NC SOUTH OF SURF CITY...1 TO 3 FT
NC NORTH OF SURF CITY INCLUDING PAMLICO/ALBEMARLE SNDS...4 TO 6 FT
SE VA AND DELMARVA INCLUDING LOWER CHESAPEAKE BAY...2 TO 4 FT
UPPER AND MIDDLE CHESAPEAKE BAY...1 TO 2 FT
LONG ISLAND SOUND AND RARITAN BAY...5 TO 10 FT
ELSEWHERE FROM OCEAN CITY MD TO THE CT/RI BORDER...4 TO 8 FT



Invest 98E

An area of low pressure centered roughly 600 miles southwest of Manzanillo is gradually showing signs of organization.



Figure 3. Latest infrared satellite image of Invest 98E. Image credit: NOAA

The upper tropospheric shear looks light, and the biggest impediment appears to be that the system is still largely embedded in the Intertropical Convergence Zone (ITCZ). The global models do not appear to be resolving this situation particularly well, as they show a quasi-stationary system that moves erratically for the next five days in response to several competing gyres within a convectively active ITCZ. For this reason, I am little more conservative than the NHC in regards to development potential.

In addition, the GFS forecasts strong northwesterly shear north of about 16N beginning in about 72 hours, which could arrest any strengthening beyond that time. The farther south the system remains, the better the surrounding environment will be.

This low is expected to move slowly toward the west-northwest, but it is possible that motion could be erratic.

Probability of development in 48 hours: 40%

2012 Atlantic hurricane season 2012 East Pacific hurricane season Hurricane Sandy Invest 98E

Updated: 7:45 AM GMT on October 28, 2012

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Tropical weather analysis - October 27, 2012

By: KoritheMan, 6:20 AM GMT on October 27, 2012

Sandy

Sandy remains a hurricane as it slowly pulls away from the Bahamas. As of the latest NHC advisory, the following information was available on the storm:

Wind: 75 mph, with higher gusts
Location: 28.1°N 76.9°W
Movement: NNE at 7 mph
Pressure: 969 mb
Category: 1 (Saffir-Simpson Hurricane Scale)

A burst of convection has occurred to the northwest of the center, but Sandy continues to be afflicted by strong vertical shear and dry air entrainment associated with an upper low near south Florida. However, analysis of water vapor imagery throughout the day suggests that this low has essentially become absorbed into Sandy, with only a small fragment of upper-level vorticity remaining in association with it.



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

Having said that, the upper tropospheric flow over Sandy appears to have relaxed a little, although enough shear and asymmetry in the convective pattern remain so that a little more weakening is anticipated, which should bring Sandy below hurricane strength over the next 12-24 hours. Beyond 36 hours, the models show Sandy entering a highly baroclinic environment, and some reintensification is shown at that time, and Sandy is forecast to be of hurricane strength when it makes United States landfall. Analysis of 0z upper air data over the United States shows a rather impressive jet streak at 300 mb over the Ohio Valley into southeastern Canada. This speed maximum, which is as high as 80-100 knots over the United States, will likely help to reinvigorate the circulation of Sandy through baroclinic (non-tropical) processes. In addition, the GFS shows vertical shear decreasing over the core of the hurricane as it nears the New England coast. All of these factors combined with sea surface temperatures that are well above average for this time of year should promote some baroclinic reintensification prior to the tropical cyclone moving inland. Global model isobaric fields suggest that Sandy could be extratropical by the time it reaches the United States, but it is simply too difficult to adequately predict the exact timing of this particular event. My personal hunch is that the warm sea surface temperatures in the region, which extend rather far to the north, will help to maintain at least a weak warm core in the system up until at least just after landfall.

Regardless of the technical status of Sandy when it makes landfall, impacts will be felt well away from the center in the form of wind, rain, coastal flooding, and some possible wet snow as the backside of the system taps into the cold air associated with the upper-level trough to the west. Given the magnitude of the shear, isolated tornadoes will be possible as well, although I suspect that these will be marginal and brief, and confined to a small area of coastal and inland areas in areas of onshore flow/higher dew points. The ambient airmass will likely be too cold to support a regional tornado outbreak, however, especially in areas north and west of the center, since they will be closer to the axis of the upper-level trough.

Sandy could push an especially high water level into Long Island, which is notoriously vulnerable to storm surge. How much water moves into Long Island/New York City will be contingent upon how far south Sandy makes landfall. Currently, the projected path of the hurricane as portrayed by both myself and the National Hurricane Center is not a particularly beneficial scenario to that island, as they will be in areas of onshore flow throughout pretty much the entire duration, even after the storm moves inland. It is simply too difficult to predict with any accuracy where Sandy will make its United States landfall.

The Bahamas are still underneath a tropical storm warning, and sustained tropical storm force conditions will probably continue lashing the central and northwestern Bahamas for the next 12 hours. Wind gusts to that strength are possible farther south in the archipelago in areas outside the tropical storm warning. These conditions will exacerbate the efforts of power crews to restore power to the electrical grid in the region.

Gusty winds will also likely continue over coastal sections of the east coast of Florida throughout the next 12 or so hours as well, but surface observations suggest that the winds in the region are below tropical storm force.

Offshore buoy observations suggest that wind gusts to near tropical storm force are located only about 75 miles from the coasts of South and North Carolina. These winds could spread onshore, particularly if the shear increases again and pushes the convection to the north side of the circulation center. Watches and warnings (see below) have been posted for this region as well.

I suspect that the watches and warnings for Florida will be discontinued later today as Sandy makes her advance toward the northeast.

Recent satellite fixes, along with comparison of this evening's microwave data, suggest that Sandy has made the expected turn toward the north-northeast. However, 0z upper air data indicated that there is enough of a ridge over the mid-Atlantic and northeastern United States to not allow for too sharp a poleward component of motion, perhaps for another 6-12 hours. After that, however, a solid turn to the northeast is expected as Sandy comes under increasing southwesterly flow associated with the eastern United States trough. However, this trough is negatively tilted, which suggests that the trough will not fully recurve Sandy. As a result, the hurricane is forecast to make a rather aclimatological bend back to the northwest and west-northwest toward the United States coast as a mid-level ridge builds to the north of the cyclone as the longwave begins to lift out toward the northeast.

5-day intensity forecast

INITIAL 10/27 0300Z 65 KT 75 MPH
12 hour 10/27 1200Z 65 KT 75 MPH
24 hour 10/28 0000Z 60 KT 70 MPH
36 hour 10/28 1200Z 60 KT 70 MPH
48 hour 10/29 0000Z 65 KT 75 MPH
72 hour 10/30 0000Z 70 KT 80 MPH...APPROACHING NEW ENGLAND
96 hour 10/31 0000Z 50 KT 60 MPH...INLAND POST-TROPICAL/EXTRATROPICAL
120 hour 11/01 0000Z 40 KT 45 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...
* FLORIDA EAST COAST FROM NORTH OF JUPITER INLET TO ST AUGUSTINE
* SOUTH SANTEE RIVER TO DUCK...INCLUDING PAMLICO
AND ALBEMARLE SOUNDS
* GREAT ABACO AND GRAND BAHAMA ISLANDS

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* SAVANNAH RIVER TO SOUTH SANTEE RIVER
* FLORIDA EAST COAST FROM NORTH OF ST AUGUSTINE TO FERNANDINA BEACH
* BERMUDA

IN ADDITION...GALE WATCHES ARE IN EFFECT FOR AREAS NORTH OF THE
TROPICAL STORM WARNING AREA. SEE STATEMENTS FROM LOCAL NATIONAL
WEATHER SERVICE FORECAST OFFICES.

INTERESTS ELSEWHERE ALONG THE EAST COAST OF THE UNITED STATES SHOULD
MONITOR THE PROGRESS OF SANDY.

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

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA.

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.

The National Weather Service in Mount Holly, New Jersey put out a rather accurate that statement that clearly portrays the enormous threat Sandy poses to the affected areas:

"PUBLIC INFORMATION STATEMENT
NATI
ONAL WEATHER SERVICE MOUNT HOLLY NJ
631 PM EDT FRI OCT 26 2012

...POTENTIAL HISTORIC STORM FOR THE AREA...

TROPICAL CYCLONE SANDY IS EXPECTED TO MOVE NORTHWARD AND THEN TAKE A
TURN BACK TO THE NORTHWEST, MAKING LANDFALL ALONG THE MID ATLANTIC
COAST. IT APPEARS THIS OCCURS SOMEWHERE BETWEEN THE DELMARVA
PENINSULA AND WESTERN LONG ISLAND.

SANDY IS EXPECTED TO INTENSIFY AS IT INTERACTS WITH AN UPPER LEVEL
SYSTEM MOVING OUT OF THE GREAT LAKES, AND INDICATIONS ARE THAT OUR
REGION MAY EXPERIENCE A WIDESPREAD DAMAGING STORM, POSSIBLY OF
HISTORIC PROPORTIONS.

WIDESPREAD DAMAGING WINDS ARE POSSIBLE. THE EXACT STORM TRACK IS
STILL UNCERTAIN AND THIS WILL DETERMINE THE ACTUAL IMPACTS. HOWEVER,
THE STORM IS FORECAST TO BE A LARGE STORM THEREFORE DO NOT FOCUS ON
THE EXACT CENTER OF THE STORM. IT APPEARS THAT THE STRONGEST WINDS
WILL OCCUR MONDAY AND TUESDAY.

IN ADDITION, WIDESPREAD HEAVY RAIN /POSSIBLY AS MUCH AS 6 TO 10
INCHES/ WOULD CAUSE SIGNIFICANT FLOODING ON RIVERS AND STREAMS
ACROSS THE REGION. THIS COULD BE MAJOR TO EVEN RECORD FLOODING.
RAIN CAN BE EXPECTED TO BEGIN DURING THE DAY SUNDAY OR SUNDAY
EVENING AND THEN CONTINUE MONDAY WHEN IT WILL BECOME HEAVY AT
TIMES. AS WATER IS PUSHED TOWARD THE COAST, COASTAL FLOODING WILL
INCREASE AND THIS COULD BE TO MAJOR TO PERHAPS EVEN RECORD LEVELS
ALONG THE COASTS OF NEW JERSEY AND DELAWARE. THE EXTENT OF THE
COASTAL FLOODING WILL BE DEPENDENT ON THE TRACK OF THE STORM.

THIS HAS THE POTENTIAL TO BE A LARGE AND RECORD SETTING STORM, WITH
WIDESPREAD WIND DAMAGE, INLAND AND COASTAL FLOODING, AND BEACH
EROSION. THE COMBINATION OF THE HEAVY RAIN AND WIND WILL CREATE THE
POTENTIAL FOR WIDESPREAD POWER OUTAGES AND SIGNIFICANT FLOODING. AT
THIS TIME, THE MOST LIKELY TIME FRAME FOR THE WORST OF THE RAIN AND
WIND LOOKS TO BE MONDAY AND TUESDAY. THIS MEANS THERE IS STILL TIME
TO PREPARE.

SOME SUGGESTED PRE-STORM ACTIONS ARE:

1. FUEL UP YOUR VEHICLES.

2. IF YOU HAVE A GENERATOR, BE SURE YOU HAVE ADEQUATE FUEL ON HAND.

3. TO PREPARE FOR THE POSSIBILITY OF PROLONGED POWER OUTAGES, MAKE
SURE YOU HAVE A SUPPLY OF FRESH BATTERIES AND A SUPPLY OF CANDLES OR
FLASHLIGHTS ON HAND.

4. BE SURE TO HAVE SEVERAL DAYS OF FRESH WATER ON HAND FOR DRINKING
AND COOKING.

5. IF YOU STILL HAVE LAWN FURNITURE OUTSIDE, SECURE OR STORE IT
INDOORS. SECURE ANY OUTSIDE ITEMS THAT COULD BECOME AIRBORNE IN
STRONG WINDS, INCLUDING HALLOWEEN DECORATIONS.

6. CLEAN OUT ANY STORM DRAINS OR GUTTERS THAT MAY BE CLOGGED BY
LEAVES.

7. IF YOU LIVE IN A FLOOD PRONE AREA AND IF POSSIBLE, CONSIDER
MOVING ITEMS THAT MAY BECOME DAMAGED TO HIGHER GROUND.

8. IF YOU HAVE LIMITED MOBILITY OR KNOW OF SOMEONE WHO MAY BE
DISABLED, CONSIDER ARRANGING FOR TEMPORARY SHELTER IF THEY LIVE IN
AN AREA THAT MAY FLOOD OR COULD LOSE POWER.

9. IF YOU NEED TO EVACUATE, BE SURE TO CARE FOR YOUR PETS.

$$

2012 Atlantic hurricane season Hurricane Sandy

Permalink

Tropical weather analysis - October 26, 2012

By: KoritheMan, 8:12 AM GMT on October 26, 2012

Sandy

Sandy continues moving across the western Atlantic as a hurricane. As of the latest NHC advisory, the following information was available on the storm:

Wind: 85 mph, with higher gusts
Location: 25.8°N 76.5°W
Movement: NNW at 13 mph
Pressure: 968 mb

Sandy is becoming increasingly less organized, which is not atypical of western Atlantic hurricanes. The convective cloud shield has become elongated south to north, and UW-CIMSS analysis shows 40 kt of southwesterly shear over the hurricane, due to an upper low over the northwestern Caribbean Sea and adjacent southern Gulf of Mexico. In addition, shortwave infrared satellite imagery suggests the southern portion of the circulation has become exposed. All of this suggests a weakening tropical cyclone.



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

Since the convection has started to spread out, the inner core of the hurricane will probably wind down soon, while the outer core becomes much larger. Since the vertical shear is forecast to remain prohibitive, and there is no reason to assume that it won't, Sandy does not seem particularly likely to restrengthen. In fact, the storm may even temporarily weaken to a tropical storm in the next day or two. In about three days, however, the hurricane is forecast to move into an environment of increasing baroclinicity, and some reintensification is anticipated beyond that time as the cyclone interacts with a negatively-tilted trough currently moving across the central United States. While some baroclinic reintensification is expected prior to US landfall, I should note that we have little skill in predicting hurricane interaction with oncoming troughs, and Sandy could easily get sheared apart by the trough, rather than strengthen. It all depends on the relative proximity between the hurricane and the trough.

Hurricane warnings are still in effect for the central and northwestern Bahamas, and this will likely be upheld for at the next 36 hours since Sandy is forecast to decelerate a bit as it makes its closest approach toward Florida. Already, tropical storm force winds have been reported across sections of Miami-Dade County. Sustained tropical storm force winds will likely only affect the far eastern portion of this county, if they are to move onshore at all. However, winds could gust to tropical storm force for the next 24 hours, and residents in the watch/warning areas across Florida should monitor the progress of Sandy.

It should be noted that with the expected shearing environment and cold waters as Sandy approaches New England, the convective pattern will become even more asymmetric and unevenly distributed than it is now. This will result in a more widespread impact than what would ordinarily be expected with a more symmetrical hurricane with a more uniform cloud structure.

Significant storm surge values can be expected, especially to the north of the center. These values will be exacerbated by the onset of the full moon, which will generate high tide in the affected areas. It should be noted that all of the models are forecasting a storm with a central pressure anywhere between 10 and 40 mb lower than the Perfect Storm of 1991, which hit around roughly the same time Sandy is projected to hit. That storm had a central pressure of 972 mb. And while the global models are not designed to handle baroclinic processes related to tropical cyclones very well, I find it difficult to believe that Sandy will not be a vigorous storm at United States landfall. Interests in the mid-Atlantic and New England should be reviewing their hurricane preparedness plans now, and should have an evacuation plan in order in case it becomes necessary at any point during this event.

In addition to the storm surge, heavy rainfall and possible inland flooding will be possible. Wind damage will be the biggest threat with Sandy by far; power outages will likely be very widespread, and anywhere between 100,000 and 1,000,000 people will probably be without electricity following the storm. Remember, it does not take much wind to topple trees and power lines that become saturated by water. While less certain, mean northwesterly flow associated with the backside of Sandy could interact with the cold air behind the trough and help to generate snowfall across interior sections of New England that are closer to the trough axis. This could aggravate power outages in the area, and hamper the efforts of power crews to restore the electricity grid in the affected areas.

0z upper air data suggests that a well-established mid-level ridge remains over the western Atlantic and northeastern United States. Concurrently, the aforementioned trough is in the process of eroding the western extent of this ridge. However, the trough is not moving very quickly, and it has been impacting the central United States for the last three days. This is why Sandy is predicted to move a little bit slower over the next 24 hours, as it will take time for the trough to win the battle and capture the storm in southwesterly flow.

The trough is forecast to bypass the hurricane in about three days, leaving Sandy to gently curve north-northwestward to northwestward into the New England states as a mid-level ridge builds in the wake of said trough. This is an unprecedented path for an October hurricane, but that won't stop it from happening.

I want to emphasize that Sandy is a very significant threat to the United States. If things pan out as forecast, the hurricane could easily be one of the worst natural disasters to impact the region in modern times.

5-day intensity forecast

INITIAL 10/26 0600Z 75 KT 85 MPH
12 hour 10/26 1800Z 70 KT 80 MPH
24 hour 10/27 0600Z 70 KT 80 MPH
36 hour 10/27 1800Z 65 KT 75 MPH
48 hour 10/28 0600Z 65 KT 75 MPH
72 hour 10/29 0600Z 70 KT 80 MPH
96 hour 10/30 0600Z 70 KT 80 MPH
120 hour 10/31 0600Z 50 KT 60 MPH...INLAND POST-TROPICAL/EXTRATROPICAL

5-day track forecast



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

Watches and warnings

A HURRICANE WARNING IS IN EFFECT FOR...
* THE NORTHWESTERN BAHAMAS EXCEPT ANDROS ISLAND

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE CENTRAL BAHAMAS
* FLORIDA EAST COAST FROM OCEAN REEF TO FLAGLER BEACH
* LAKE OKEECHOBEE
* ANDROS ISLAND IN THE NORTHWESTERN BAHAMAS

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* FLORIDA EAST COAST FROM NORTH OF FLAGLER BEACH TO FERNANDINA BEACH
* FLORIDA UPPER KEYS FROM OCEAN REEF TO CRAIG KEY
* FLORIDA BAY

INTERESTS ELSEWHERE ALONG THE EAST COAST OF THE UNITED STATES SHOULD
MONITOR THE PROGRESS OF SANDY. WATCHES AND WARNINGS WILL LIKELY BE
REQUIRED FOR PORTIONS OF THIS AREA EARLY FRIDAY MORNING.

A HURRICANE WARNING MEANS THAT HURRICANE CONDITIONS ARE EXPECTED
SOMEWHERE WITHIN THE WARNING AREA. PREPARATIONS TO PROTECT LIFE AND
PROPERTY SHOULD BE RUSHED TO COMPLETION.

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

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA.

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.

2012 Atlantic hurricane season Hurricane Sandy

Permalink

Tropical weather analysis - October 25, 2012

By: KoritheMan, 9:48 AM GMT on October 25, 2012

Sandy

Sandy rapidly intensified into a strong Category 2 hurricane over the last several hours, and subsequently moved over eastern Cuba. As of the latest NHC advisory, the following information was available on Sandy:

Wind: 105 mph, with higher gusts
Location: 20.9N 75.8W
Movement: N at 18 mph
Pressure: 954 mb
Category: 2 (Saffir-Simpson Hurricane Scale)

Sandy has fared surprisingly well during its passage over eastern Cuba. The eye is still well-defined in both satellite and Camaguey radar data, notwithstanding a bit of warming cloud tops. Upper-level outflow remains well-defined, especially to the north, where it extends all the way to near Bermuda.



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

Objective analysis of areal sea surface temperatures indicate that Sandy will remain over some rather warm waters after it emerges from the coast of Cuba. Also, while some southwesterly shear still appears to be affecting Sandy, the hurricane is moving in roughly the same direction as the primary shear vector, which will likely minimize the impact of the shear. The GFS actually shows a pretty favorable upper wind environment remaining over the hurricane for about another day, which could allow the storm to become a major hurricane while moving through the southern Bahamas. This could be a particularly dangerous situation for them, as the the shear will not have kicked in enough to significantly alter disrupt Sandy's inner core structure and unevenly distribute the associated wind field and convective structure. Beyond 24 hours, southwesterly to southerly shear is forecast to increase dramatically as an upper-level trough over the central United States moves eastward. Beyond 48 hours, water temperatures should fall to about 26C, and the combination of these factors are expected to weaken the hurricane.

The global models still show Sandy losing tropical characteristics as it gets north of 35N. This is a reasonable prognosis, but coastal and offshore buoys still show some rather warm water temperatures in the mid-Atlantic/New England region, with 60F sea surface temperatures extending as far north as Rhode Island. This is rather unusual for this time of year, and this could delay the transition process, and potentially allow Sandy to remain a warm-core system all the way up to landfall. This would be most unorthodox for late October, but stranger things have happened.

Regardless of the technical status of the storm, Sandy is expected to pose a major wind damage threat to New England, and I suspect damage will be comparable to a major hurricane if the current forecast verifies.

In the meantime, hurricane conditions will likely continue over far northeastern Cuba, and these winds will begin spreading into the Bahamas later this morning. Sustained winds could approach the bottom of Category 3 strength over the southern and central Bahamas, and even if they don't, wind gusts will easily exceed 100 mph. Residents in that archipelago should be rushing their hurricane preparation to completion; since the entire island chain is under a hurricane warning, even areas outside the path of the eye should take Sandy very seriously.

Tropical storm warnings are up for a portion of the Florida east coast, and interests across that half of the peninsula should carefully monitor the progress of Sandy. I suspect sustained tropical storm force winds will remain just offshore, especially since Sandy's inner core remains well-defined from its tussle with eastern Cuba, which of course means a less broad tropical storm force wind field. In addition, since the upper tropospheric flow over the western Atlantic is forecast to be mostly from the south or southwest, there appears to be little chance of the convection wrapping into the western quadrant and that becoming the dominant portion of the circulation. Nevertheless, there is enough uncertainty that people there should be aware. At the very least, winds will be gusty, and tropical storm force wind gusts are still possible, particularly in the warning area.

I suspect the tropical storm warning for Haiti will be discontinued with the next advisory as Sandy continues to move well away from that country.

Water vapor, upper air, and UW-CIMSS data indicate that the hurricane is embedded in a large-scale weakness associated with the central United States trough. The global models suggest that this pattern will cause Sandy to move generally northward through the Bahamas, then turn northeastward. There remains some significant disagreement amongst the global models after 72 hours, with the GFS calling for Sandy to move northeastward to a position well offshore Maine and Atlantic Canada. However, this model has come back west at 0z, and now sends the storm into Maine beyond day five. The HWRF shoots Sandy out to sea. The ECMWF, which has been very consistent, pulls Sandy into New England on Monday evening. By the same token, the GFS, which in itself has proven to be very reliable after the upgrade this year, has been just as consistent with an out to sea scenario. The differences amongst the guidance appears to be related primarily to how Sandy interacts with the trough. Unfortunately, I am no messiah, and cannot with complete accuracy predict how things are going to evolve. However, based on the 500 mb wind fields in most of the global models, as well as the synoptic flow pattern over the northern United States, which would favor a more northward trough, I tend to favor the ECMWF option.

Interests in the mid-Atlantic and New England should carefully monitor the progress of Sandy over the next several days. Interests in Atlantic Canada should also monitor it, as there is enough margin for error that they may see a landfall.

My forecast track is in good agreement with the latest National Hurricane Center track.

5-day intensity forecast

INITIAL 10/25 0900Z 90 KT 105 MPH...EMERGING FROM THE COAST OF CUBA
12 hour 10/25 1800Z 100 KT 115 MPH...OVER WATER
24 hour 10/26 0600Z 95 KT 110 MPH
36 hour 10/26 1800Z 90 KT 105 MPH
48 hour 10/27 0600Z 80 KT 90 MPH
72 hour 10/28 0600Z 70 KT 80 MPH
96 hour 10/29 0600Z 70 KT 80 MPH
120 hour 10/30 0600Z 65 KT 75 MPH...POST-TROPICAL/EXTRATROPICAL

5-day track forecast



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

Watches and warnings


A TROPICAL STORM WATCH HAS BEEN ISSUED FOR THE NORTHEASTERN FLORIDA
COAST FROM FERNANDINA BEACH SOUTHWARD TO NORTH OF FLAGLER BEACH.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A HURRICANE WARNING IS IN EFFECT FOR...
* CUBAN PROVINCES OF CAMAGUEY...LAS TUNAS...GRANMA...SANTIAGO DE
CUBA...HOLGUIN...AND GUANTANAMO
* THE RAGGED ISLANDS IN THE SOUTHEASTERN BAHAMAS
* THE CENTRAL BAHAMAS
* THE NORTHWESTERN BAHAMAS

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* HAITI
* FLORIDA EAST COAST FROM OCEAN REEF TO FLAGLER BEACH
* LAKE OKEECHOBEE
* THE REMAINDER OF THE SOUTHEASTERN BAHAMAS

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* FLORIDA EAST COAST FROM NORTH OF FLAGLER BEACH TO FERNANDINA BEACH
* FLORIDA UPPER KEYS FROM OCEAN REEF TO CRAIG KEY
* FLORIDA BAY

INTERESTS ELSEWHERE ALONG THE SOUTHEASTERN COAST OF THE UNITED
STATES SHOULD MONITOR THE PROGRESS OF SANDY.

A HURRICANE WARNING MEANS THAT HURRICANE CONDITIONS ARE EXPECTED
SOMEWHERE WITHIN THE WARNING AREA. PREPARATIONS TO PROTECT LIFE AND
PROPERTY SHOULD BE RUSHED TO COMPLETION.

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA...IN THIS CASE WITHIN
24 TO 36 HOURS.

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA.

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.

2012 Atlantic hurricane season Hurricane Sandy

Permalink

Tropical weather analysis - October 24, 2012

By: KoritheMan, 11:29 AM GMT on October 24, 2012

Sandy

Tropical Storm Sandy is intensifying. As of the latest NHC advisory, the following information was posted on the system:

Wind: 70 mph, with higher gusts
Location: 16.3°N 77.0°W
Movement: N at 14 mph
Pressure: 986 mb

Sandy may already be a hurricane based on the improving satellite presentation; a ragged eye has recently become established, with convection in the developing eyewall wrapping around this feature. The 6z Dvorak estimates would support hurricane strength as well.



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

Environmental conditions remain favorable for intensification until Sandy reaches the coast of Jamaica later today, although there is some southwesterly shear impacting the storm, as evidenced by the squashed outflow pattern in that direction. It appears to be caused by a weak upper low over the northwestern Caribbean Sea. After reaching Jamaica, the cyclone should weaken a bit due to interaction with mountainous eastern Cuba as well as increasing vertical shear. However, the global models suggest that Sandy will begin deriving substantial baroclinic energy once over the western Atlantic as it interacts with the central United States trough, which is expected to keep the winds to near hurricane force throughout the forecast period. It is difficult to predict structural and intensity changes due to baroclinic processes, but it is likely that Sandy will shed at least some of its tropical characteristics. In addition, the southwesterly flow associated with the trough will likely keep the strongest winds and heaviest rains to the east and northeast of the low-level center. Before the flow becomes too prohibitive, however, Sandy could come close enough to south Florida to bring a brief period of tropical storm force winds. Barring significant changes to the large-scale pattern, sustained tropical storm force winds will likely stay just offshore, as suggested by the GFDL. However, there is enough potential for error so that interests in this area, as well as the Florida Keys, should monitor the progress of Sandy over the next couple of days. The Bahamas will also likely get a several day period of tropical storm force winds beginning on Thursday afternoon.

Sandy is forecast to lose tropical characteristics in five days, although it is difficult to specifically predict the timing and magnitude of such events.

Sandy is moving rather quickly toward the north as it becomes embedded within the large-scale southerly flow associated with a developing trough over the central United States. The global models suggest a continuation of the current motion throughout the next few days. This should take the center over eastern Jamaica later today, and across eastern Cuba tonight. I am quite confident in the early portion of the forecast given the simplicity of the synoptic pattern as well as the strong model agreement. Once the system enters the western Atlantic, the forecast becomes riddled with a bit more uncertainty due to the dichotomous nature of the track models. The ECMWF, which has historically been very reliable (albeit the GFS has trumped it in virtually every way this year), takes Sandy inland over the northeastern United States as a rather potent low pressure system; the NOGAPS shows a similar scenario. The GFS, CMC, HWRF, and GFDL keep Sandy offshore. These important differences seem to be primarily to how the depth of the central United States trough.

While the amplitude of this trough perhaps isn't the most impressive, I've also seen worse. In such a scenario, the best thing to do is to go with a blend of the various model solutions, both of which are equally viable at this time. My forecast track is similar to, but a little left of the National Hurricane Center track, and is not as fast as the recurvature camp of models.

Given the uncertainty, and the fact that Sandy has the potential to be a rather significant storm -- tropical or not -- for the region, interests in the mid-Atlantic and New England should carefully monitor future forecasts on Sandy. Always consult your local National Weather Service forecast office for information specific to your area.

5-day intensity forecast

INITIAL 10/24 0900Z 60 KT 70 MPH
12 hour 10/24 1800Z 70 KT 80 MPH...AT THE JAMAICAN COAST
24 hour 10/25 0600Z 70 KT 80 MPH...INLAND OVER EASTERN CUBA
36 hour 10/25 1800Z 65 KT 75 MPH...OVER WATER
48 hour 10/26 0600Z 65 KT 75 MPH
72 hour 10/27 0600Z 60 KT 70 MPH
96 hour 10/28 0600Z 60 KT 70 MPH
120 hour 10/29 0600Z 60 KT 70 MPH...POST-TROPICAL/EXTRATROPICAL

5-day track forecast



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

Watches and warnings

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A HURRICANE WARNING IS IN EFFECT FOR...
* JAMAICA
* CUBAN PROVINCES OF CAMAGUEY...LAS TUNAS...GRANMA...SANTIAGO DE
CUBA...HOLGUIN...AND GUANTANAMO

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* HAITI
* THE CENTRAL BAHAMAS...INCLUDING CAT ISLAND...THE EXUMAS...LONG
ISLAND...RUM CAY...AND SAN SALVADOR.

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* THE SOUTHEASTERN AND NORTHWESTERN BAHAMAS
* FLORIDA EAST COAST FROM JUPITER INLET TO OCEAN REEF
* FLORIDA UPPER KEYS FROM OCEAN REEF TO CRAIG KEY
* FLORIDA BAY

A HURRICANE WARNING MEANS THAT HURRICANE CONDITIONS ARE EXPECTED
SOMEWHERE WITHIN THE WARNING AREA. PREPARATIONS TO PROTECT LIFE
AND PROPERTY SHOULD BE RUSHED TO COMPLETION.

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA...IN THIS CASE WITHIN
24 TO 36 HOURS.

A TROPICAL STORM WARNING MAY BE REQUIRED FOR THE NORTHWESTERN
BAHAMAS LATER THIS MORNING.

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 48 HOURS.

A TROPICAL STORM WATCH MAY BE REQUIRED FOR PORTIONS OF EAST-CENTRAL
FLORIDA LATER THIS MORNING.

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.



Tony

Tropical Storm Tony formed late Tuesday from what was previously Tropical Depression Nineteen. As of the latest NHC advisory, the following information was available on the storm:

Wind: 45 mph, with higher gusts
Location: 27.4°N 47.9°W
Movement: ENE at 16 mph
Pressure: 1003 mb

Tony still appears to be strengthening, with the center embedded in the eastern portion of the central dense overcast.



Figure 3. Latest infrared satellite image of Tropical Storm Tony. Image credit: NOAA

There is an interesting thing to note with Tony this morning. A 0900Z SSMI microwave pass suggested a small upper-level eye feature, albeit a tad open, particularly to the east. An eye has not popped out in conventional satellite images, which has resulted in Dvorak numbers that are largely unchanged. However, I am going to assume that the eye is not transient, and that it will soon appear in geostationary satellite pictures. Based on this, my intensity forecast is a little higher than that of the National Hurricane Center as of 9z. Since these mid-latitude cyclones often interact with troughs, sudden episodes of intensification like the one Tony appears to be experiencing are more common than not. Tony's window of opportunity for strengthening is quickly closing, however, as water vapor imagery shows fast southwesterly upper-level winds approaching the tropical storm. These winds are forecast to increase this evening as the trough to the west of the storm strengthens its influence. The global models suggest that Tony will begin interacting with this trough in about 24 hours, which is expected to cause extratropical transition in about 36 hours. Tony is forecast to become absorbed by the trough/baroclinic zone in about four days, also in agreement with the global model guidance.

Water vapor imagery and UW-CIMSS data suggest little change to the large-scale steering pattern surrounding the storm. Tony is expected to continue accelerating east-northeastward in the mid-latitude westerly flow associated with the trough to its west. My forecast track is similar but a little to the left of the National Hurricane Center 0900Z forecast package given current movement trends, which appear to be a little to the left of the forecast points.

5-day intensity forecast

INITIAL 10/24 0900Z 40 KT 45 MPH
12 hour 10/24 1800Z 50 KT 60 MPH
24 hour 10/25 0600Z 45 KT 50 MPH
36 hour 10/26 1800Z 40 KT 45 MPH...POST-TROPICAL/EXTRATROPICAL
48 hour 10/27 0600Z 35 KT 40 MPH...POST-TROPICAL/EXTRATROPICAL
72 hour 10/28 0600Z 35 KT 40 MPH...POST-TROPICAL/EXTRATROPICAL
96 hour 10/29 0600Z...ABSORBED BY LARGER EXTRATROPICAL LOW

5-day track forecast



Figure 4. My 5-day forecast track for Tony.

2012 Atlantic hurricane season Tropical Storm Sandy Tropical Storm Tony

Updated: 12:21 PM GMT on October 24, 2012

Permalink

Tropical weather analysis - October 23, 2012

By: KoritheMan, 6:30 AM GMT on October 23, 2012

Sandy

Tropical Storm Sandy formed over the southwest Caribbean on Monday. As of the latest NHC advisory, the following was posted on Sandy:

Wind: 45 mph, with higher gusts
Location: 12.9°N 78.7°W
Movement: Stationary
Pressure: 998 mb

Sandy is an intensifying tropical cyclone. The tropical storm appears to be quickly developing a central dense overcast, and the associated convection is quite vigorous at this time. A large curved band has become apparent east of the center; I expect this band will wrap cyclonically into the center during the overnight hours, and probably help to invigorate the circulation even more.



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

Sandy is currently in a very favorable for strengthening, even rapid. The SHIPS rapid intensification parameter at 0z shows a 45% chance of a 35 kt increase in wind speed during the next 24 hours. This model is generally good at recognizing when the large scale environment is conducive to such episodes, and looking at water vapor imagery, a well-defined anticyclonic pattern aloft has set up over Sandy. In addition, the underlying waters are very warm, and extent to a rather large depth. Finally, the ambient area encompassing Sandy is extremely moist. Climatologically, this area has bred some rather infamous hurricanes this time of year, the most recent being Hurricane Paloma in 2008. Sandy may be no exception. Interestingly, water vapor imagery shows a newly-developed upper low centered over central Cuba. The GFS insists that this feature will weaken and move eastward, but this does not appear to be happening at the present time, and even if it does, the low is distant enough from Sandy so that it will provide more diffluence than shear, which is evident by the expanding outflow in the western quadrant of the storm. This feature could play a major role in rapid intensification of the storm during the next 24 hours.

While I am not going to go all the way to 85 kt in 24 hours (which would be a 45 kt increase, complimenting the SHIPS), that degree of intensification is entirely possible if current trends continue. My intensity forecast is just shy of this threshold, and shows an intensifying hurricane making landfall in Jamaica in 48 hours. There is a chance Sandy could become a major hurricane prior to reaching Jamaica. Thereafter, interaction with Jamaica and Cuba, along with a significant increase in vertical shear, should be enough to progressively weaken Sandy. The global models generally show Sandy losing tropical characteristics near the end of the forecast period, so a transition into a subtropical storm is shown at day five.

Water vapor, UW-CIMSS steering data, and upper air data suggest that Sandy is south of a well-established mid-level ridge over the western Atlantic. The net result has been a practically stationary tropical cyclone. A weak shortwave trough is getting ready to move off the United States east coast, and the southwesterly flow associated with this feature is expected to turn Sandy to the north-northeast later today. While the large-scale models are in good agreement on this, there are still some notable differences after the system emerges from northern Cuba. The ECMWF brought the system rather close to the Florida east coast at 12z, and the GFS, which had previously insisted on a trajectory that carried the system out to sea on a path well to the east of Florida, has also moved a little farther westward in the longer range. I mentioned in my last forecast that Sandy could take a similar trajectory to Hurricane Michelle in 2001, and the models have started to reflect that thinking. It should be noted that there is considerable uncertainty in long-range forecasts.

My own track forecast is similar to the National Hurricane Center except a little slower during the first 48 hours, and farther west after that.

Sandy is expected to produce torrential rains over portions of Haiti, Jamaica, and eastern Cuba. On the current track, rainfall will be limited in the Cayman Islands since they will be on the weaker side of the storm.

5-day intensity forecast

INITIAL 10/23 0300Z 40 KT 45 MPH
12 hour 10/23 1200Z 50 KT 60 MPH
24 hour 10/24 0000Z 65 KT 75 MPH
36 hour 10/24 1200Z 80 KT 90 MPH...SOUTH OF JAMAICA
48 hour 10/25 0000Z 70 KT 80 MPH...INLAND OVER JAMAICA
72 hour 10/26 0000Z 60 KT 70 MPH...OVER WATER
96 hour 10/27 0000Z 50 KT 60 MPH
120 hour 10/28 0000Z 50 KT 60 MPH...SUBTROPICAL

5-day track forecast



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



Tropical Depression Nineteen

Tropical Depression Nineteen also formed on Monday, and as of the latest NHC advisory, the following was available on the cyclone:

Wind: 35 mph, with higher gusts
Location: 23.0°N 51.8°W
Movement: N at 9 mph
Pressure: 1006 mb

Deep convection has developed over the low-level center this morning, which is an indication that the tropical cyclone is getting better organized. Unfortunately, there have been no new microwave passes to fully ascertain the inner structure of the cyclone.



Figure 3. Latest infrared satellite image of Tropical Depression Nineteen. Image credit: NOAA

Vertical shear is currently fairly light over the system, and the underlying waters are warm. This should allow for some strengthening of the tropical cyclone for the next 36-48 hours. Subsequently, the global models show the shear significantly increasing as the storm begins to interact with a large extratropical low. Concurrent with decreasing sea surface temperatures, the system is forecast to become extratropical in about three days, and then become absorbed by the aforementioned non-tropical system at day five.

The depression appears to be in the process of recurving, as the motion no longer looks uniformly northward. A turn to the northeast is expected to begin later today, followed by acceleration as the westerlies pick up the storm. The upper-level trough forecast to perform the recurve is a relatively shallow one, but it should still prove adequate to cause the depression to exit the stage. Although the four day forecast point shows a tropical cyclone nearing the Azores, the depression is forecast to become absorbed by the north Atlantic extratropical cyclone before it can make landfall in that archipelago.

5-day intensity forecast

INITIAL 10/23 0300Z 30 KT 35 MPH
12 hour 10/23 1200Z 35 KT 40 MPH
24 hour 10/24 0000Z 40 KT 45 MPH
36 hour 10/24 1200Z 45 KT 50 MPH
48 hour 10/25 0000Z 50 KT 60 MPH
72 hour 10/26 0000Z 45 KT 50 MPH...EXTRATROPICAL
96 hour 10/27 0000Z 35 KT 40 MPH...EXTRATROPICAL
120 hour 10/28 0000Z...ABSORBED BY EXTRATROPICAL LOW

5-day track forecast



Figure 4. My 5-day forecast track for Tropical Depression Nineteen.



Eastern Pacific disturbance

An area of disturbed weather continues several hundred miles south-southwest of Acapulco. This system has not become any better organized over the last 24 hours, and although the shear is light, the large size of the disturbance appears to be inhibiting development.

This low is expected to move westward and still has the potential for some development, but nothing interesting is likely to happen for at least the next three days.

The global models are less enthusiastic about the threat to Baja, probably because they depict a system that is slower to develop. That seems like the more realistic in light of current organization trends.

Probability of development in 48 hours: 20%

2012 Atlantic hurricane season 2012 East Pacific hurricane season Tropical Storm Sandy Tropical Depression Nineteen

Updated: 7:02 AM GMT on October 23, 2012

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Tropical weather analysis - October 21, 2012

By: KoritheMan, 3:36 AM GMT on October 22, 2012

Invest 99L

A tropical wave over the central Caribbean Sea continues producing a large area of showers and thunderstorms, primarily northeast of the wave axis.



Figure 1. Latest infrared satellite image of Invest 99L. Image credit: NOAA

As alluded to above, the associated shower activity is located primarily in a band north and northeast of the center. I attribute this to a little bit of northwesterly shear on the northeastern periphery of an upper-level anticyclone centered just to the southwest of the center of this tropical disturbance. Despite continuous forecasts from the GFS of a lighter upper tropospheric shear regime over the last several days, this has so far not materialized, as the anticyclone and the invest have never become collocated. It is a bit

interesting to note, however, that said anticyclone appears to be just a little bit closer to the tropical wave axis today than has been the general motif over the last several days.

Assuming this trend continues, 99L should be able to gain some organization. Right now, however, the surface circulation is not closed, and the associated convection remains poorly-organized. Development is certainly not imminent.

I should note that even if the shear lessens, I do not see the most favorable environment for our would be tropical cyclone; the upper wind environment shown on the GFS is still fairly zonal, which suggests that there will be a battle between diffluence and shear. I think the shear will triumph, effectively preventing much in the way of intensification while the system traverses the Caribbean. Once over the western Atlantic in about four days, however, conditions could become a little more favorable. There is still a chance this system could eventually attain hurricane status, but the odds of this appear substantially low for the Caribbean portion of the system's lifespan.

The track of this system continues to be much more muddled than the intensity forecast. How ironic. While the models are, in general, in relatively good agreement on taking the system across eastern Cuba and into the western Atlantic well east of the eastern United States, there have been some periodic westward shifts over the last couple of days, enough that I want to alert south Florida to be watching this system. Actually, the entire eastern seaboard should, with the greatest threat area being New England based on the large scale pattern.

12z and 0z upper air data suggest that a low- to mid-level ridge is building over the western Atlantic in the wake of a shortwave trough currently in the vicinity of Bermuda. This should cause a continued slow westward motion of the disturbance, followed by a virtual stall beginning tomorrow morning and persisting for about 24 hours or so after that. Thereafter, the models obviously insist on recurvature subsequent to the Cuba crossing, but I am a little skeptical of this, as there appears to be no obvious large-scale features capable of lifting the system out to the northeast so quickly; the flow over much of the central and southern United States is zonal, which implies synoptic scale ridging. Thus, I have some concern -- not overly, but enough -- that there will be enough ridging to force the system dangerously close to the coast of south Florida prior to the arrival of a potent shortwave trough forecast to enter the central plains in about four to five days. Based on the pattern, I can see a repeat of 2001's Hurricane Michelle, which brought tropical storm force winds to portions of south Florida as it more or less grazed the peninsula. For this reason, I am just a little bit to the left of the model consensus, but am still siding with the recurvature option for now.

This system could still become a tropical depression during the next day or two. An alternate scenario is that significant development does not occur until the system reaches the western Atlantic.

In the meantime, regardless if the system develops or not, it is expected to produce heavy rains over portions of Jamaica, the Cayman Islands, and Cuba over the next couple of days.

These rains could produce localized flooding and mudslides in areas of mountainous terrain.

Probability of development in 48 hours: 70%



Invest 90L

An area of low pressure moving across the central Atlantic is associated with a tropical wave interacting with an upper tropospheric cold low. Satellite pictures this evening reveal a system that is much better organized than yesterday. Convection has developed over the low-level center, although earlier microwave data and recent satellite fixes suggest that the associated thunderstorms remain disorganized.



Figure 3. Latest infrared satellite image of Invest 90L. Image credit: NOAA

While there is currently not much vertical shear over the system, water vapor imagery and UW-CIMSS vorticity data suggest that it is sitting directly underneath the upper low that was orbiting to the south of 90L yesterday. The magical no shear barrier this low is furnishing should gradually give way to less favorable conditions beginning Tuesday afternoon as the upper low weakens, probably due to latent heat release from 90L's thunderstorms. There is still the potential for some development to occur during this narrow window.

This system is not a threat to land.

Probability of development in 48 hours: 40%



Pacific disturbance

A large area of disturbed weather in the eastern Pacific located about 425 miles southeast of Acapulco continues to produce a large area of showers and thunderstorms, although this activity remains poorly-organized. There is some modest easterly shear over the system, but it is not strong enough to arrest development. No, the bigger factor arguing against immediate development is the large size of the disturbance, which will undoubtedly take some time to conglomerate and flourish.

This system is expected to move generally westward over the next couple of days. Longer term, the models still suggest it could pose a threat from southern Baja to southwest Mexico.

Probability of development in 48 hours: 20%

2012 East Pacific hurricane season 2012 Atlantic hurricane season Invest 99L Invest 90L

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Tropical weather analysis - October 20, 2012

By: KoritheMan, 12:39 AM GMT on October 21, 2012

Invest 99L

An area of low pressure over the central Caribbean Sea is primarily associated with a tropical wave. While the associated shower activity has diminished this evening, this is most likely attributable to the ordinary diurnal convective minimum period, and the system as a whole appears to be organizing.



Figure 1. Latest infrared satellite image of Invest 99L. Image credit: NOAA

Surface pressures are falling in the area, which is a sign of a developing system. However, there is still some westerly shear over the system, as evidenced by high cloud motions derived from satellite pictures. This is associated with the northern periphery of an anticyclone to the south of Invest 99L. If the GFS is correct, this feature will collocate with 99L over the next day or so as the system as a whole moves off toward the west. Longer term, the models are unanimous in suggesting that a deep-layer trough emerging from the Great Lakes in about a week will be sufficient to recurve the system. More specifically, it appears that the trough that is currently off the eastern seaboard will join the large upper low over the north Atlantic southeast of Greenland, and the enhanced southwesterly flow with these two features will keep a residual weakness in place before the arrival of the Great Lakes trough; the latter feature then prevents a ridge from rebuilding in to the north. An alternate scenario, supported by some of the GFS ensembles, is that the system could come a little closer to south Florida than currently predicted. I consider this to be an outlier scenario for now.

The GFS 850-200 mb upper wind fields suggest that upper-level winds could once again become unfavorable in about four days, which should prevent 99L from rapidly intensifying as so many systems in the past have done in this area. While there is still some chance of a hurricane, I do not consider the idea of anything stronger than a Category 1 of much merit due to close proximity of the system to strong upper-level shear. The, GFS suggests that there will be a lot of westerly shear for 99L to contend with after it enters the western Atlantic. In theory, this sort of speed maximum could cause more divergence than shear, depending on its relative proximity to 99L; this could suggest some reintensification over that portion of the basin, but it is simply impossible to predict the specifics of such an event right now.

Environmental conditions appear favorable for a tropical depression to form over the next day or two.

Regardless of development, heavy rainfall capable of causing flash flooding and mudslides are likely over portions of Hispaniola, Jamaica, the Cayman Islands, and Cuba over the next several days as the low moves off toward the west, then north.

Probability of development in 48 hours: 60%



Invest 90L

A tropical wave interacting with an upper low over the central Atlantic about 1000 miles east-northeast of the northern Leeward Islands has become a little better organized over the last several hours.



Figure 3. Latest infrared satellite image of Invest 90L. Image credit: NOAA

Convection remains minimal at this time, but upper-level winds are forecast to become more favorable for development over the next couple of days, which should allow for some development. The system is currently in close proximity to an upper low, which is orbiting just to the south of the circulation center associated with the tropical wave. How much interaction occurs between the two features will determine whether or not any development that occurs from this wave is tropical or subtropical. Right now, given forecasts from the global models as well as current trends, I feel that the upper low will steadily distance itself from 90L as the wave axis moves west-northwestward. While this is is the expected evolution, things can change, and my best guess is that the upper low will act to keep some degree of vertical shear over the disturbance regardless.

Recurvature should begin at around roughly 72 hours as the deep-layer trough off the United States east coast moves eastward.

Probability of development in 48 hours: 30%



Gulf of Tehuantepec disturbance

An area of disturbed weather has formed in the far eastern Pacific several hundred miles south of the Gulf of Tehuantepec. Upper-level winds appear favorable for gradual development of this area as it moves generally westward. Long range forecasts from the global models suggest another possible threat to Baja at longer ranges, but it is too early to be confident of this.

Probability of development in 48 hours: 20%

2012 Atlantic hurricane season 2012 East Pacific hurricane season Invest 99L Invest 90L

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Tropical weather analysis - October 16, 2012

By: KoritheMan, 7:40 AM GMT on October 16, 2012

Rafael

Rafael became the ninth hurricane of the 2012 Atlantic hurricane season late on Monday evening. As of the 2:00 AM NHC intermediate advisory, the following information was available on Rafael:

Wind: 85 mph, with higher gusts
Location: 25.9°N 65.3°W
Movement: NNE at 14 mph
Pressure: 974 mb
Category: 1 (Saffir-Simpson Hurricane Scale)

The cloud pattern associated with the hurricane has changed little over the last few hours. Microwave and conventional satellite images show that the eyewall is intense in the northern and western quadrants, but is open to the south and east. In addition, the lower- and middle-level circulations appear to have a noticeable vertical tilt, probably due to about 30 knots of southwesterly shear analyzed by the SHIPS and UW-CIMSS.



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

Water vapor images suggest that an upper trough moving into the western Atlantic and the mid-oceanic trough are acting together to shear Rafael. The shear is forecast to increase further in about 24 hours as the former trough makes its way eastward, which is expected to induce some weakening of the hurricane. In the meantime, however, Rafael has about another 12-24 hours to intensify before the shear becomes prohibitive. There is a chance that Rafael could briefly become a Category 2 hurricane. Extratropical transition is expected just beyond 48 hours as Rafael interacts with a strong upper-level trough and associated frontal zone over the western Atlantic.

The hurricane has turned toward the north-northeast as it comes increasingly under the influence of the western Atlantic trough. Rafael is forecast to execute a gentle recurvature around the east side of this trough. Beyond 48 hours, global model fields suggest that the hurricane will begin interacting with a vigorous extratropical cyclone currently moving through Quebec. Right now it appears that Rafael will eventually take the frontier and absorb the low. However, there may be some slow motion near the end of the period, at least relative to the acceleration being experienced now, which is shown in the track forecast below.

A tropical storm warning is in effect for Bermuda, and interests there should monitor the progress of Rafael over the next 24 hours.

5-day intensity forecast

INITIAL 10/16 0600Z 75 KT 85 MPH
12 hour 10/16 1800Z 80 KT 90 MPH
24 hour 10/17 0600Z 80 KT 90 MPH
36 hour 10/17 1800Z 75 KT 85 MPH
48 hour 10/18 0600Z 70 KT 80 MPH
72 hour 10/19 0600Z 60 KT 70 MPH...POST-TROPICAL/EXTRATROPICAL
96 hour 10/20 0600Z 55 KT 65 MPH...POST-TROPICAL/EXTRTRAOPICAL
120 hour 10/21 0600Z 50 KT 60 MPH...POST-TROPICAL/EXTRATROPICAL

5-day track forecast



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



Paul

Paul unexpectedly became the fifth major hurricane of the 2012 Eastern Pacific hurricane season on Monday afternoon, but has since weakened to a Category 2 hurricane. As of the latest NHC intermediate advisory, the following information was made available on the hurricane:

Wind: 110 mph, with higher gusts
Location: 20.9°N 113.1°W
Movement: NNE at 17 mph
Pressure: 967 mb
Category: 2 (Saffir-Simpson Hurricane Scale)

Southerly shear is beginning to increase over the hurricane due to the combination of a mid-level ridge over central Mexico and a mid- to upper-level trough over the western United States. While the cloud pattern remains reasonably well-organized for the moment, if one looks closely, it is apparent that the convection on the southwest side is becoming elongated, which is evident in a 0446 UTC AMSU microwave image; the outflow appears to be fading in that direction as well. This likely signifies the beginning of the end for Paul.



Figure 3. Latest infrared satellite image of Hurricane Paul. Image credit: NOAA

Since a further increase in the shear appears to be imminent, Paul is expected to weaken at a faster rate in about 24 hours. Having said that, Paul is still expected to be of hurricane strength when it makes landfall in central Baja Tuesday evening or early Wednesday morning. Interaction with the mountains of that peninsula, as well as strong vertical shear, are forecast to lead to an eventual demise of the tropical cyclone. Dissipation is shown at day three.

Paul remains on track, albeit possibly about 15 miles farther east than the current NHC forecast track. The global models remain in reasonable agreement on the track, with the primary differences being how far Paul moves inland before turning back to the west around the north side of an upper low forecast to develop from the western United States trough. My thinking is pretty similar to the National Hurricane Center.

Because of the forecast track, tropical storm and hurricane warnings have been issued for portions of the Baja Peninsula (see below). Interests in the warned area, especially in the hurricane warning area, should be taking Paul very seriously. The rugged terrain of the Baja Peninsula means that winds will increase with height, especially in wind gusts. Residents living in these hilly areas should prepare for damaging winds and flash flooding due to orographic lift and its enhancing effect on precipitation levels. At the coast, damaging winds, storm surge, and heavy rainfall will be the primary concern. Some waterspouts may also occur and attempt to move inland.

All in all, Paul is not an atypical hurricane for the peninsula, and it is not something they cannot deal with.

The one good bit of news with Paul is that it is a relatively compact hurricane; hurricane force winds currently extend outward up to only 30 miles from the center, while tropical storm force winds extend outward up to 90 miles. This should minimize the wind hazard relative to a much larger hurricane, and it could also minimize the rainfall potential. However, satellite imagery shows a band of heavy convection has detached from the inner circulation of Paul and is lashing southern and central Baja with locally heavy rains. Since Paul is moving quickly, weather conditions in the peninsula will worsen quickly, as early as 12 to 18 hours from now. Preparations to protect life and property should be rushed to completion, as such preparation becomes difficult subsequent to the onset of tropical storm force winds, which begins at 39 mph.

5-day intensity forecast

INITIAL 10/16 0600Z 95 KT 110 MPH
12 hour 10/16 1800Z 85 KT 100 MPH
24 hour 10/17 0600Z 70 KT 80 MPH...APPROACHING CENTRAL BAJA
36 hour 10/17 1800Z 50 KT 60 MPH...INLAND
48 hour 10/18 0600Z 30 KT 35 MPH...OVER WATER
72 hour 10/19 0600Z...DISSIPATED

5-day track forecast



Figure 4. My 5-day forecast track for Paul.

Watches and warnings


A HURRICANE WARNING IS IN EFFECT FOR THE...
* WEST COAST OF BAJA CALIFORNIA FROM SANTA FE NORTHWARD TO PUNTA
ABREOJOS

A TROPICAL STORM WARNING IS IN EFFECT FOR THE ...
* WEST COAST OF BAJA CALIFORNIA NORTH OF PUNTA ABREOJOS TO EL POCITO
* WEST COAST OF BAJA CALIFORNIA SOUTH OF SANTA FE TO AGUA BLANCA
* EAST COAST OF BAJA CALIFORNIA FROM LA PAZ TO BAHIA SAN JUAN
BAUTISTA

A TROPICAL STORM WATCH IS IN EFFECT FOR THE...
* WEST COAST OF BAJA CALIFORNIA NORTH OF EL POCITO TO PUNTA EUGENIA

A HURRICANE WARNING MEANS THAT HURRICANE CONDITIONS ARE EXPECTED
SOMEWHERE WITHIN THE WARNING AREA. A WARNING IS TYPICALLY ISSUED...
IN THIS CASE WITHIN 24 HOURS...BEFORE THE ANTICIPATED FIRST
OCCURRENCE OF TROPICAL-STORM-FORCE WINDS...CONDITIONS THAT MAKE
OUTSIDE PREPARATIONS DIFFICULT OR DANGEROUS. PREPARATIONS TO
PROTECT LIFE AND PROPERTY SHOULD BE RUSHED TO COMPLETION.

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

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 48 HOURS.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA..PLEASE MONITOR PRODUCTS
ISSUED BY YOUR NATIONAL METEOROLOGICAL SERVICE.

2012 Atlantic hurricane season 2012 East Pacific hurricane season Hurricane Rafael Hurricane Paul

Updated: 8:33 AM GMT on October 16, 2012

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Tropical weather analysis - October 15, 2012

By: KoritheMan, 5:06 AM GMT on October 15, 2012

Rafael

Tropical Storm Rafael is near hurricane strength as of the latest NHC advisory:

Wind: 70 mph, with higher gusts
Location: 21.6°N 64.8°W
Movement: NNW at 10 mph
Pressure: 989 mb

Rafael is displaying a much better organized satellite appearance this evening. Convection has developed much closer to the center, with the deepest convection lying in a band just to the north of it.



Figure 1. Latest infrared satellite image of Tropical Storm Rafael. Image credit: NOAA

Satellite estimates do not quite support hurricane strength, and earlier reconnaissance data suggests that Rafael is just shy of it. An eye is not yet apparent using conventional or microwave satellite fixes. While some degree of southwesterly shear continues to affect Rafael, water vapor imagery suggests that it is not enough to prevent additional strengthening. The upper environment ahead of Rafael, while not the best I've seen, is definitively not unfavorable. It should be noted that if the cyclone tracks west of the forecast track, it could get a little stronger than indicated below; such a path would also delay extratropical transition by about a day.

Rafael is moving toward a break in the subtropical ridge. This weakness is due to an advancing shortwave upper-level trough progressing through the eastern United States. Said weakness shows up nicely just to the west of 70W. UW-CIMSS steering data suggests that as the trough swings eastward, the weakness is doing likewise. This pattern is expected to turn Rafael toward the north, then northeast. This is consistent with the global models, which reflect a tightly packed consensus. It should be noted that there are still some differences in forward speed, primarily in response to how quickly Rafael responds to the large-scale flow associated with the trough, but since the GFS and ECMWF have come into better agreement on the forward speed, and since the speed differences aren't that drastic, the forecast track is more certain tonight in terms of forward speed.

A tropical storm watch has been issued for Bermuda. It appears unlikely they will have a hurricane watch since Rafael is expected to remain well to the east of the island at its point of closest approach.

5-day intensity forecast

INITIAL 10/15 0300Z 60 KT 70 MPH
12 hour 10/15 1200Z 65 KT 75 MPH
24 hour 10/16 0000Z 70 KT 80 MPH
36 hour 10/16 1200Z 75 KT 85 MPH
48 hour 10/17 0000Z 70 KT 80 MPH
72 hour 10/18 0000Z 60 KT 70 MPH
96 hour 10/19 0000Z 55 KT 65 MPH...POST-TROPICAL/EXTRATROPICAL
120 hour 10/20 0000Z 50 KT 60 MPH...POST-TROPICAL/EXTRATROPICAL

5-day track forecast



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



Paul

Paul is just below hurricane strength according to the latest NHC advisory:

Wind: 70 mph, with higher gusts
Location: 15.8°N 115.3°W
Movement: NNW at 7 mph
Pressure: 991 mb

Paul appears to be strengthening. An earlier SSMI pass just before 0z suggested an eye and a formative eyewall. Subsequent images have indicated a further increase in organization, with convection wrapping more around the southern side of the eye than in the first image. Additionally, the CDO has begun to exhibit more of a banded appearance around what will likely be an eye on conventional satellite images.



Figure 2. Latest infrared satellite image of Tropical Storm Paul. Image credit: NOAA

With little apparent shear over Paul, there seems to be no obvious reason why the cyclone will not strengthen. Paul has about another 18-24 hours over warm waters and light shear. This should result in intensification, and Paul is forecast to become a hurricane soon. I mentioned in my last forecast that Paul had a faint chance of becoming a major hurricane. However, that was predicated on the assumption that it would strengthen, when it actually hesitated a bit during subsequent advisories. Since Paul will be over cool waters in about a day, this opportunity appears to have ended. In addition to the gradually cooling sea surface temperatures, the GFS shows vertical shear increasing sharply beyond 24 hours. This combination is expected to result in a steady decay of the cyclone, with remnant low status now depicted at day four.

A combination of microwave and satellite fixes suggest that Paul has turned northward. I have very little disagreement with the National Hurricane Center forecast track this evening, with a continued general northward motion anticipated for the next 48 hours. After that, there have been some changes after the system approaches Baja. In general, the models have trended westward over the past several cycles, and now show the system remaining just offshore. Looking at the trough today, it is not as impressive as it was yesterday, and with a more zonal regime setting up over California and Oregon, Paul will probably not recurve into Baja. However, I recall a similar forecast scenario with Hurricane Bud all the way back in May, which was forecast to remain offshore but did not. There is enough margin for error that interests in central Baja should monitor the progress of Paul until it has safely passed.

Right now, it does not appear that appreciable mid-level moisture from Paul will make into the southwestern United States and enhance rainfall potential there.

5-day intensity forecast

INITIAL 10/15 0300Z 60 KT 70 MPH
12 hour 10/15 1200Z 70 KT 80 MPH
24 hour 10/16 0000Z 75 KT 85 MPH
36 hour 10/16 1200Z 65 KT 75 MPH
48 hour 10/17 0000Z 50 KT 60 MPH
72 hour 10/18 0000Z 40 KT 45 MPH
96 hour 10/19 0000Z 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW
120 hour 10/20 0000Z...DISSIPATED

5-day track forecast



Figure 4. My 5-day forecast track for Paul.

2012 Atlantic hurricane season 2012 East Pacific hurricane season Tropical Storm Rafael Tropical Storm Paul

Updated: 5:29 AM GMT on October 15, 2012

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Tropical weather analysis - October 13, 2012

By: KoritheMan, 4:40 AM GMT on October 14, 2012

Rafael

Tropical Storm Rafael continues to move across the eastern Caribbean. As of the most recent NHC advisory, the following was posted on the storm:

Wind: 50 mph, with higher gusts
Location: 18.4°N 63.6°W
Movement: N at 14 mph
Pressure: 1004 mb

The center of the cyclone is a little difficult to locate this evening, but using a slew of satellite and radar fixes as well as a partial 0z SSMIS microwave pass, it appears to be embedded within the convection, albeit the western edge of it.



Figure 1. Latest infrared satellite image of Tropical Storm Rafael. Image credit: NOAA

Convection has increased this evening, but the strongest thunderstorms continue to be confined to some rather vigorous banding east of the center. In short, it means that Rafael is still suffering from some shear. However, since the shear appears to be slowly decreasing as forecast, Rafael still has a chance to strengthen. Most of the guidance makes Rafael a hurricane, and I see no apparent reason why this should not happen. However, since the tropical cyclone is expected to be intensifying as it nears Bermuda, Rafael may not quite be a hero in a half shell. An alternate scenario is for Rafael to fail to reach hurricane strength due to the large outer wind maxima. Based on the shear forecast from the GFS, and the overt sign of improving upper-level conditions, I consider this to be an outlier scenario at this time.

Extratropical transition is shown at day four as the cyclone encounters cold waters and the core of the mid-latitude westerlies. None of the guidance really shows Rafael gaining or maintaining any strength subsequent to extratropical transition. Given that these processes are already difficult to predict at actual time of the event, I am not about to try predicting them now, so it seems prudent to follow the models in this instance.

Determining the initial motion of Rafael has been a rather excruciating process this evening, in part due to the center being embedded within at least some of the convective canopy. My best estimate is just west of north. Water vapor imagery shows a mid- to upper-level trough in the same general longitude as the tropical storm. This trough is forecast to bypass Rafael, temporarily providing a low amplitude ridge to the north. In fact, there is evidence of this ridge beginning to build now. In about a day, however, southwesterly mid-level flow is forecast to increase over the western Atlantic as an upper trough and associated cold front now over the central United States moves eastward. This should trigger the onset of recurvature in about 36 hours. While the global models are in good agreement on the projected heading, they differ significantly in terms of the expected forward speed of the cyclone. The GFS and CMC remain the fastest and farthest north, while the ECMWF is considerably slower and much farther south than the other models. The rather quick forward motion favored by the former camp is predicated on the assumption of a stronger Rafael, which will have more proclivity to move in tandem with the trough.

Since these models appear to have a realistic presentation on the future intensity of Rafael, and also because climatology favors it, I tend to give more weight to the GFS scenario.

In the meantime, I feel that the building ridge to the north of Rafael will force the storm a little more toward the west before the pull of the trough becomes manifest.

5-day intensity forecast

INITIAL 10/14 0300Z 45 KT 50 MPH
12 hour 10/14 1200Z 50 KT 60 MPH
24 hour 10/15 0000Z 55 KT 65 MPH
36 hour 10/15 1200Z 60 KT 70 MPH
48 hour 10/16 0000Z 70 KT 80 MPH
72 hour 10/17 0000Z 70 KT 80 MPH
96 hour 10/18 0000Z 60 KT 70 MPH...POST-TROPICAL/EXTRATROPICAL
120 hour 10/19 0000Z 50 KT 60 MPH...POST-TROPICAL/EXTRATROPICAL

5-day track forecast



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

Tropical storm force winds have already been reported across some of the northern Leeward Islands this evening. These conditions are expected to continue for the next 12-24 hours, along with very heavy rain. Given the intense convection Rafael is generating, flash flooding may become a concern.

A hurricane watch may be required for Bermuda in about 24-36 hours.

Watches and warnings


A TROPICAL STORM WARNING IS IN EFFECT FOR...
* CULEBRA AND VIEQUES
* U.S. VIRGIN ISLANDS
* BRITISH VIRGIN ISLANDS
* ANGUILLA...BARBUDA...ST. KITTS... NEVIS...ANTIGUA...AND MONTSERRAT
* SABA...ST. EUSTATIUS...AND ST. MAARTIN
* ST. MARTIN
* GUADELOUPE...DESIRADE...LES SAINTES...MARIE GALANTE

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* PUERTO RICO

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA...IN THIS CASE WITHIN THE
NEXT 12 TO 24 HOURS.

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA.

INTERESTS IN BERMUDA SHOULD MONITOR THE PROGRESS OF RAFAEL.



Paul

Tropical Storm Paul quickly formed Saturday aftenroon from what was Invest 97E. As of the latest NHC advisory, the following information was available on Paul:

Wind: 50 mph, with higher gusts
Location: 14.2°N 114.1°W
Movement: W at 13 mph
Pressure: 1001 mb

Satellite pictures this evening reveal that Paul is an intensifying tropical cyclone. The central dense overcast is well-established and slowly becoming more symmetrical, and outer banding remains well-defined in the western semicircle, although it has decreased a little this evening.



Figure 3. Latest infrared satellite image of Tropical Storm Paul. Image credit: NOAA

Paul has about 36 hours before it crosses the 26C isotherm. Under light shear and little evidence of dry air, there is little reason why the storm will not continue intensifying during this period. Indeed, the SHIPS shows Paul reaching Category 2 strength at the end of that period, while the LGEM is just shy of that intensity. While I normally don't put much emphasis on the SHIPS intensity forecasts since they are usually based on persistence, in this case it might actually be right. That model shows a 66% chance of a 30 kt increase in wind speed during the next 24 hours, which is a distinct possibility if Paul develops an inner core. Like with Miriam, there is an outside chance that Paul briefly becomes a major hurricane.

Beyond 48 hours, Paul will encounter a hostile environment characterized by increasing southwesterly to southerly shear, cooler waters, and some rather stable thermodynamics, especially by 72 hours. This is expected to dissipate the cyclone at the end of the forecast period.

Paul is on the south side of a low- to mid-level ridge, while a strong upper trough is amplifying upstream. Since Paul is vertically coherent, it should begin to gain latitude soon, responding to the southerly flow induced by the aforementioned trough. A slow recurvature toward Baja is expected. While the global models are in relative agreement on the overall track philosophy, there are some significant differences in the forward speed, characterized by how soon Paul makes the expected turn to the northeast. I will compromise between the GFS and ECMWF solutions, since these models are typically top-performing, and because both options appear to have some truth to them. However, given the depth of the trough seen on water vapor images, I will pull the storm inland over central Baja at day four, before bringing it back out over water at day five. All in all, my forecast track is very similar to that of the National Hurricane Center.

With the magnitude of destructive shear forecast, it is possible that Paul could shear apart sooner than indicated below.


5-day intensity forecast

INITIAL 10/14 0300Z 45 KT 50 MPH
12 hour 10/14 1200Z 55 KT 65 MPH
24 hour 10/15 0000Z 75 KT 85 MPH
36 hour 10/15 1200Z 80 KT 90 MPH
48 hour 10/16 0000Z 70 KT 80 MPH
72 hour 10/17 0000Z 50 KT 60 MPH...APPROACHING CENTRAL BAJA
96 hour 10/18 0000Z 35 KT 40 MPH...INLAND
120 hour 10/19 0000Z 30 KT 35 MPH...OVER WATER

5-day track forecast



Figure 4. My 5-day forecast track for Paul.

2012 Atlantic hurricane season 2012 East Pacific hurricane season Tropical Storm Rafael Tropical Storm Paul

Updated: 4:43 AM GMT on October 14, 2012

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Tropical weather analysis - October 12, 2012

By: KoritheMan, 7:21 AM GMT on October 12, 2012

Patty

Tropical Storm Patty formed over the Bahamas on Thursday morning from what was formerly known as Invest 97L. As of the 11:00 PM NHC advisory, the following information was available on the cyclone:

Wind: 45 mph, with higher gusts
Location: 25.9°N 72.5°W
Movement: Stationary
Pressure: 1005 mb

Satellite pictures indicate that Patty's center has become exposed to the southwest of a rather amorphous mass of deep convection; this exposure was evident on a 0100Z SSMIS overpass as well.



Figure 1. Latest infrared satellite image of Tropical Storm Patty. Image credit: NOAA

With 30 knots of shear over Patty, it is hard to envision it persisting much longer. Water vapor imagery shows an upper low developing off the Florida coast. The GFS elongates this feature, but keeps enough cyclonic vorticity lingering over the western Atlantic to continue shearing Patty. As if that weren't enough, Patty is expected to move directly into the shear vector. Finally, there is a lot of dry air in neighboring areas of the western Atlantic. These factors are expected to lead to a quick demise of the tropical cyclone with the system expected to become a remnant low in about 48 hours. Patty is forecast to completely lose its identity in about five days, but it could occur a little sooner.

Patty's motion had been difficult to determine, but with the exposed center, this has become a less daunting task. The center appears to be a little farther south than estimated by the National Hurricane Center in the 11:00 PM advisory, but that does not translate to a significant southward movement of the tropical storm; more likely, the center was estimated to be too far north.

Patty appeared to move southwestward for a time, but has since become stationary again. Patty is caught in a rather complex steering pattern, with a ridge located on either side of the tropical cyclone. In addition, water vapor imagery shows a large amplitude trough remains quasi-stationary in the same general location as the tropical storm. However, 0z upper air data from the eastern United States suggests that the weakness associated with the trough is confined primarily above 500 mb. While the cyclone center could easily move back underneath the convection and cause Patty to move in fits and wobbles as it responds to the trough, in general the shear is expected to be too prohibitive to allow Patty to remain embedded in the deep convection. The exposed nature of the circulation as well as the relatively southerly location of the cyclone seems to assure that Patty will not respond much to the trough. However, I am not confident enough to state this definitively, and with the GFS showing a northeastward movement during the last two cycles, the best course of action seems to be to show a stationary movement for the next 24 hours or so. After that time, Patty is expected to begin moving more steadily to the southwest, with some acceleration expected later in the period.

5-day intensity forecast

INITIAL 10/12 0300Z 40 KT 45 MPH
12 hour 10/12 1200Z 40 KT 45 MPH
24 hour 10/13 0000Z 35 KT 40 MPH
36 hour 10/13 1200Z 35 KT 40 MPH
48 hour 10/14 0000Z 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW
72 hour 10/15 0000Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
96 hour 10/16 0000Z 20 KT 25 MPH...POST-TROPICAL/REMNANT LOW
120 hour 10/17 0000Z...DISSIPATED

5-day track forecast



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



Invest 98L

A vigorous tropical wave accompanied by a surface low pressure center approaching the Windward Islands ("98L") continues to show signs of organization. More specifically, the center appears to be very near Saint Lucia based on a north wind from that island, as well as satellite, radar, and microwave data.



Figure 3. Latest infrared satellite image of Invest 98L. Image credit: NOAA

I note that the convection is well-removed from the center due to southwesterly shear. It is possible a new center could form underneath that convection within the mid-level circulation, but there is currently no evidence remotely supporting this. Upper-level winds are forecast to gradually improve over the next 24-36 hours as the upper low over the central Caribbean Sea moves westward and provides a more diffluent upper tropospheric flow. Based on this, which appears to be realistic given current trends, I expect additional slow organization of 98L over the next day or two, and it could become a tropical depression in a couple of days.

The track still remains a little tricky this morning. The dynamical models still insist on bringing the system well to the east of Puerto Rico. While they are more reasonable this morning than they have been, insofar as them actually predicting a motion into the eastern Caribbean, I still feel they are a little too far east based on climatology, the continued more west than north movement with this system (current satellite imagery depicts more of a west-northwest) motion, rather than northwest, and also because the system is so far south. Having said that, I feel that 98L could come closer to Puerto Rico than the models are currently thinking, and interests there should monitor it as much as the neighboring islands should.

Subsequent to crossing the Leeward Islands, the models forecast a large-amplitude trough will capture the system and recurve it. However, this is not expected to be a particularly sharp recurve; a decent analog for this storm, except perhaps a little farther east, would be Hurricane Kyle from 2008.

Regardless of development, heavy rain and strong gusty winds will overspread much of the Windward and Leeward Islands over the next day or two. This weather could eventually spread into the US Virgin Islands and Puerto Rico, and interests in the aforementioned areas should carefully monitor the progress of this system, which is likely to become a tropical cyclone in the eastern Caribbean.

Surface observations from Barbados suggest that winds to tropical storm force have already begun lashing that island, with a wind gust to 40 mph reported over the last hour. These winds will gradually permeate the rest of the islands as 97L moves into the eastern Caribbean.

Probability of development in 48 hours: 70%



Invest 97E

An area of low pressure over the eastern Pacific located about 450 miles south of Manzanillo has become better organized over the last 24 hours.



Figure 4. Latest infrared satellite image of Invest 97E. Image credit: NOAA

While the system is currently experiencing a bit of easterly shear, perhaps a consequence of the Gulf of Mexico ridge, the GFS suggests that the upper flow pattern will improve some over the next couple of days, enough to potentially allow for some development. It should be noted that that model does not call for an anticyclonic upper air environment, so rapid intensification of this disturbance is not currently anticipated. But then, we also have little skill in deducing these events.

This low could pose a long range threat to southern Baja, but the GFS and ECMWF suggest it will turn away as it weakens at the last minute. However, it is too early to be confident of this.

Probability of development in 48 hours: 50%

2012 Atlantic hurricane season 2012 East Pacific hurricane season Tropical Storm Patty Invest 98L Invest 97E

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Tropical weather analysis - October 10, 2012

By: KoritheMan, 3:14 AM GMT on October 11, 2012

Invest 97L

An area of low pressure about 250 miles east of the central Bahamas is showing signs of organization this evening. I had dropped this system in my blog yesterday, as I felt it was in the process of getting absorbed into the cold front over the western Atlantic.

Instead, satellite images show a small low-level center that appears to be embedded near the area of coldest cloud tops.



Figure 1. Latest infrared satellite image of Invest 97L. Image credit: NOAA

Surface observations, microwave data, and an earlier ASCAT pass provide ample evidence of a well-defined surface circulation in the system, although the ASCAT pass suggested that the winds are not particularly strong, even when accounting for the low bias of the instrument.

Westerly shear continues over the area, and earlier microwave data suggested that the low- and mid-level centers were displaced about 15 to 20 miles eastward, no doubt as a direct result of the shear. There seems to be little chance of 97L amounting to much, as the low is forecast to lose what little upper support it has tomorrow. Since this is a small system, and because it is not moving much, any subtle increase in the shear will probably result in immediate decapitation. There is also a lot of dry air over the western Atlantic, which is another factor that argues against significant organization.

97L is caught in weak steering currents; water vapor imagery and analysis from UW-CIMSS indicate that a low- to mid-level ridge is present over Texas, while a trough is over the western Atlantic just to the north of 97L. A shot of shortwave energy diving into New England could reinforce the cyclonic vorticity/large-scale troughing in this area over the next 24-48 hours. However, 97L is a small system that may not fully respond to the trough. In addition, the expected increase in vertical shear tomorrow will probably strip the invest of most of its convection, which I believe will prevent 97L from moving in tandem with the front. Finally, 97L is isolated from most synoptic steering influences; if it were getting absorbed by the front we would expect to see some kind of evidence for that, like a northeast movement. There's nothing. I note that the upper-level outflow is being stretched from southwest to northeast, however, and as long as that remains the case, and with the front in such close proximity, the potential still exists for 97L to become absorbed. There is some model support today -- quite a bit actually -- of the system moving back toward the southwest under the low-level ridge. However, upper-level winds are forecast to be rather hostile over the Gulf of Mexico, and not very favorable in the western Caribbean either. This should preclude any sort of tropical development.

Regardless of development, locally heavy rainfall may come back for round two over portions of the central and southern Bahamas over the next day or two as the system begins to move off to the southwest.

Probability of development in 48 hours: 20%



Invest 98L

A large area of low pressure associated with a vigorous tropical wave is located about 475 miles east-southeast of the Windward Islands. While this disturbance is by no means organized, satellite pictures do suggest some evidence of very slow consolidation.



Figure 2. Latest infrared satellite image of Invest 98L. Image credit: NOAA

Looking at high cloud vectors on satellite and water vapor imagery this evening, the shear does not look as strong as it did 24 hours ago; the mid- to upper low that was responsible for it is moving westward through the northern Leeward Islands. This has resulted in the strongest shear being on the western side of the gyre. The GFS still suggests, in contrast to the SHIPS, that the upper tropospheric flow will gradually relax over the next 48-72 hours, giving way to a more diffluent -- but perhaps not anticyclonic -- environment. Based on this, as well as the fact that the mean vertical shear appears to be less than I expected in my last update, I anticipate some additional organization of 98L. There are a couple of factors that argue against rapid development: the first is the large nature of the circulation envelope. The second is that the system is still below 10N. Ideally, it will need to gain a little more latitude in order to begin taking full advantage of the Earth's Coriolis force.

Right now, the system appears to be moving slowly toward the west -- more specifically, on a direction just north of west. Based on the current steering pattern, a more definitive motion toward the west-northwest should begin shortly. The model consensus continues to bring the system into the northern Leeward Islands this weekend. While for now all of the dynamical and global models don't really bring this system into the Caribbean, I am having a hard time buying such a sharp northwestward motion given the retrograding upper low, as well as the general reluctance of 98L to gain latitude.

Regardless of development, interests in the Leeward Islands should closely monitor the progress of this system. Just in case the system tracks farther south than the dynamical models are indicating (which I do think is possible), interests in Puerto Rico and the Dominican Republic should monitor the progress of this system as well.

The low is expected to produce very heavy rains and gusty winds as it moves through the islands, even if development does not occur -- whether or not this weather is concentrated near or to the east of the low will depend on how much shear it encounters.

It should be noted that a couple of buoys well north of the center have been reporting wind gusts to tropical storm force in the vigorous convective band to the north.

Probability of development in 48 hours: 50%



Invest 97E

A broad area of low pressure is located over much of the eastern Pacific. Earlier microwave data was highly unimpressive, to say the least. Large-scale data suggest that this low is composed of a broad area of low pressure embedded in the Intertropical Convergence Zone (ITCZ), and there may be multiple swirls orbiting within the larger scale low.



Figure 3. Latest infrared satellite image of Invest 97E. Image credit: NOAA

Upper-level winds still appear favorable for development, although the enormous size and lack of definitive organization of the disturbance suggests that any development will be slow.

The GFS and ECMWF continue to develop this system in about four days, but they differ on the threat to Baja. The former keeps a more zonal regime situated north of the disturbance, which would portend a track away from Baja. The latter model shows a more meridional flow associated with the west coast trough, which would of course favor a more northward component of motion, closer toward Baja. It is impossible to identify which of these scenarios is most plausible at this time.

Interests in southern Baja should monitor the progress of this disturbance as it moves westward and eventually west-northwestward.

Probability of development in 48 hours: 20%

2012 Atlantic hurricane season 2012 East Pacific hurricane season Invest 97L Invest 98L Invest 97E

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Tropical weather analysis - October 10, 2012

By: KoritheMan, 7:50 AM GMT on October 10, 2012

Invest 98L

A vigorous tropical wave over the central Atlantic located about 750 miles east of the Windward Islands is producing a large area of showers and thunderstorms.



Figure 1. Latest infrared satellite image of Invest 98L. Image credit: NOAA

While the shear is not prohibitively strong yet, water vapor imagery suggests that southwesterly shear lies just ahead. The GFS suggests a small anticyclone will try to establish itself atop the low-level center during the next 24 hours, but I question the authenticity of this. The wave and its embedded low pressure center only have about another 12-24 hours before the shear increases. After 72 hours, there is no unity between the GFS and the SHIPS, with the latter model indicating that a ginormous shear wall will prevent 98L from developing. The former, which experience has shown to generally be more reliable, suggests that the shear may lessen a little as the system approaches the Leeward Islands. How favorable the environment becomes as the tropical wave approaches the islands is strongly contingent on how the system interacts with the mid-oceanic trough; a scenario where the tropical wave axis moves closer to the upper-level trough would obviously result in a much higher magnitude of vertical shear, while a situation where the low is equidistant to the trough would result in a more diffluent, less sheared upper wind pattern.

The track models are fairly unified in tracking the system into the northern Leeward Islands in the next 4 - 5 days. After that time, the guidance becomes a little divergent, but in general, they suggest that a strong upper-level trough forecast to amplify over the western Atlantic will be sufficient to recurve 98L well east of the United States. This would tend to fit the climatological motif for a storm forming in this area of the world during the middle of October. However, fairly strong hurricanes can still develop in the eastern Caribbean this late in the year, as most recently demonstrated with Hurricane Tomas in 2010. While I doubt 98L will become another Tomas, interests in the Leeward Islands should monitor its progress, as if the GFS is correct, the upper-level environment could become a little more favorable for development as the system approaches the archipelago; this scenario would potentially place an intensifying tropical cyclone in the vicinity of Puerto Rico and the northern Leeward Islands.

Regardless of development, this system is expected to produce heavy rainfall and gusty winds across much of the Lesser Antilles beginning in about 3 days. These rains could cause flooding in some areas.

Probability of development in 48 hours: 20%



Invest 97E

An area of disturbed weather has developed several hundred miles south of the coast of Mexico. Upper-level winds appear favorable for slow development of this broad disturbance over the next couple of days as it moves generally westward.

The majority of global models develop this low into a tropical cyclone in about 3 - 5 days, and then show a possible threat to Baja.

Probability of development in 48 hours: 10%

2012 Atlantic hurricane season 2012 East Pacific hurricane season Invest 98L Invest 97E

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Tropical weather analysis - October 8, 2012

By: KoritheMan, 5:37 AM GMT on October 08, 2012

Invest 97L

A weak area of low pressure centered near the central Bahamas continues to produce disorganized showers and thunderstorms.



Figure 1. Latest infrared satellite image of Invest 97L. Image credit: NOAA

Westerly shear continues to afflict the system, as high as 25 kt according to analyses from UW-CIMSS. Since the shear is forecast to continue, little additional organization is expected, although the system will likely continue to produce intermittent bursts of deep convection, in part due to the large-scale diffluent flow associated with the western Atlantic trough.

A northwest wind from Providenciales in the Turks and Caicos Islands suggests that 97L possesses a somewhat better organized wind field than yesterday. Since the shear is forecast to increase over the next 24 hours, I do not expect this circulation to become too much more vigorous.

Regardless of development, locally heavy rain and potentially gusty winds in thunderstorms will continue impacting portions of the Bahamas over the next day or two.

This system is forecast to begin recurving on Monday.

Probability of development in 48 hours: 10%



Olivia

Olivia remains a tropical storm as of the latest NHC advisory:

Wind: 60 mph, with higher gusts
Location: 16.2°N 120.9°W
Movement: N at 7 mph
Pressure: 998 mb

The tropical storm consists of a circular area of deep convection with minimal banding features.



Figure 1. Latest infrared satellite image of Tropical Storm Olivia. Image credit: NOAA

Since the shear does not appear prohibitively strong yet, Olivia could still gain some strength during the next 12-24 hours. However, there is enough displacement in the vertical circulations that it would be a bit of a surprise if Olivia became a hurricane. Beyond 24 hours, the shear is forecast to increase and the cyclone is expected to move across cooler waters. The cyclone is forecast to dissipate sooner than yesterday, with remnant low status shown at day three, and identity diffusion shown by day five.

A mid-level ridge over central Mexico is exhibiting a rather substantial weakness. This is due to a quasi-stationary upper low off the California coast supporting a southward-extending frontal trough. This is responsible for the current northward motion, which is easily discernible even with nighttime imagery. This general motion at roughly the same forward speed is forecast to continue for the next 24 hours. Subsequent to that time, Olivia is forecast to weaken and gradually turn to the west-southwest. The global model guidance continues to be in good agreement on the track philosophy, which appears to be relatively straightforward.

My forecast track is similar to the National Hurricane Center track.

5-day intensity forecast

INITIAL 10/08 0300Z 50 KT 60 MPH
12 hour 10/08 1200Z 55 KT 65 MPH
24 hour 10/09 0000Z 55 KT 65 MPH
36 hour 10/09 1200Z 50 KT 60 MPH
48 hour 10/10 0000Z 40 KT 45 MPH
72 hour 10/11 0000Z 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW
96 hour 10/12 0000Z 20 KT 25 MPH...POST-TROPICAL/REMNANT LOW
120 hour 10/13 0000Z...DISSIPATED

5-day track forecast



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



Elsewhere

The GFS model continues to predict the development of a tropical cyclone somewhere in the Caribbean Sea in the general range of 7 to 14 days. As of the 0z run, the target was the eastern Caribbean. The storm takes a similar path to Hurricane Omar of 2008, although of a much less severe intensity. Put simply, there is far too much run to run variability amongst the GFS with regards to the timing and placement of this feature to justify any sort of immediate concern at the moment. Presumably, this development comes from a tropical wave all the way out near 30W. This wave appears to have a fairly vigorous cyclonic circulation at the mid-levels based on analysis of satellite imagery, so it will need to be monitored as it gets farther west.

On the Pacific side, that model suggests that the tropical wave approaching Panama and Costa Rica will serve as the focal point for the development of a new tropical cyclone south of the Gulf of Tehuantepec in about four days. The ECMWF also developed this wave at 12z, albeit a few days later, and farther west. There will be a trough along the west coast of the United States capable of turning the system to the north at longer ranges, but the timing and placement of this possible tropical cyclone relative to the trough is simply too uncertain to adequately determine if a portion of southwest Mexico or Baja will be threatened.

2012 Atlantic hurricane season 2012 East Pacific hurricane season Invest 97L Tropical Storm Olivia

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Tropical weather analysis - October 7, 2012

By: KoritheMan, 5:42 AM GMT on October 07, 2012

97L

A weak area of low pressure located about 150 miles east of the Turks and Caicos Islands (Invest "97L") is producing only minimal shower activity.



Figure 1. Latest infrared satellite image of Invest 97L. Image credit: NOAA

There are no signs of organization at this time, and I am finding evidence of only a very weak circulation. Based on analysis of shortwave infrared satellite imagery, a secondary center, more specifically a mid-level vortex, is located a couple hundred miles northwest of where the low-level center is estimated to be. Convection has ignited near this vortmax, but there is no evidence of a developing surface circulation in this area based on surface observations from Nassau. There are also no signs of pressure falls in the region, which signifies the system is going nowhere fast.

Upper-level winds are not conducive for development, with the current cloud pattern portraying a proclivity toward westerly shear. I do not see the shear relaxing very much, as a large upper-level trough dominates the Gulf of Mexico and western Atlantic. In fact, it may actually increase some in about 48 hours.

I do not anticipate significant development of this system. Based on model guidance and low and mid-level steering forecasts from PSU, this system should move west-northwestward for the next 24-36 hours before beginning to recurve.

Locally heavy rainfall may impact portions of the Bahamas during the next day or two, but that is expected to be 97L's only legacy.

Probability of development in 48 hours: 10%



Olivia

Tropical Storm Olivia is intensifying as of the latest National Hurricane Center (NHC) advisory:

Wind: 50 mph, with higher gusts
Location: 14.0°N 120.5°W
Movement: W at 10 mph
Pressure: 1000 mb

There was new microwave data shortly after 0000 UTC, but unfortunately, it missed the tropical storm. Notwithstanding the absence of more recent microwave data, Olivia appears to be organizing on satellite images, with the low-level center estimated to be firmly embedded within a developing central dense overcast.



Figure 2. Latest infrared satellite image of Tropical Storm Olivia. Image credit: NOAA

Olivia appears to be sitting beneath a well-established upper tropospheric anticyclone. The GFS/SHIPS show the environment remaining anticyclonic for about 72 hours, although the cyclone is forecast to encounter cooler water before then. That is expected to combine with the marginal thermodynamic environment from about 125W westward and onset a weakening trend beyond 36 hours; southwesterly shear should also increase after the 72 hour point. The intensity guidance remains in good agreement on Olivia intensifying in the short-term, and there is a chance it could be fairly brisk. Olivia is forecast to dissipate by the end of the period.

Water vapor images and steering data from UW-CIMSS suggest that a substantial mid-level ridge is in place to the north of Olivia. The southeast flow on the south side of this ridge is expected to move the cyclone west-northwest, then northwest through 48 hours. After that time, the tropical storm is forecast to steadily become shallower and turn to the southwest under the lower tropospheric steering flow. The model guidance remains in relatively good agreement on the overall track. My own track is a little to the right of the National Hurricane Center in anticipation that Olivia will gain a little more latitude due to a weakness in the subtropical ridge, especially above 500 mb.

5-day intensity forecast

INITIAL 10/07 0300Z 45 KT 50 MPH
12 hour 10/07 1200Z 50 KT 60 MPH
24 hour 10/08 0000Z 60 KT 70 MPH
36 hour 10/08 1200Z 70 KT 80 MPH
48 hour 10/09 0000Z 65 KT 75 MPH
72 hour 10/10 0000Z 45 KT 50 MPH
96 hour 10/11 0000Z 30 KT 35 MPH
120 hour 10/12 0000Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW

5-day track forecast



Figure 3. My 5-day forecast track for Olivia.



Elsewhere

Aside from 97L, the Atlantic is quiet. However, the GFS has been consistent in developing a tropical cyclone somewhere in the Caribbean, although there are great timing and location differences, with some runs suggesting formation in the central Caribbean, and others suggesting formation in the western Caribbean. Climatology favors the latter. Considering the MJO is forecast to move back into our area of the world in the next week or two, this area will need to be watched. If the system forms in the western Caribbean, it may meander enough to become a hurricane, whereas a system developing in the central Caribbean would be less likely to develop into anything significant.

On the Pacific side, the GFS insists that Paul is not far behind, with a tropical cyclone forecast to develop south of the Mexican coast in about a week. It is too early to tell if this system would threaten land.

2012 Atlantic hurricane season 2012 East Pacific hurricane season Invest 97L Tropical Storm Olivia

Updated: 5:54 AM GMT on October 07, 2012

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Tropical weather analysis - October 3, 2012

By: KoritheMan, 4:27 AM GMT on October 04, 2012

Nadine is heading toward a landfall in the Azores. It is expected to deliver tropical storm and/or gale (depending on the status of the cyclone) conditions to the islands tonight. I will not bother writing another forecast on this already long-lived storm, as satellite data suggests the storm is rapidly losing tropical characteristics. Nadine fought the good fight, finished the race, and kept the faith.



Oscar

The curse has been broken! Here's a reward for you! For the first time in history, List 4 of the Atlantic hurricane naming lists has caught up to the other five lists and now has the recognition of having the 'O' storm. Tropical Storm Oscar developed this evening from what was previously Tropical Depression Fifteen. As of the latest NHC advisory, the following information was available on Oscar:

Wind: 40 mph, with higher gusts
Location: 19.3°N 42.2°W
Movement: NNW at 12 mph
Pressure: 1006 mb

Despite the upgrade, Oscar is not well-organized. Wind shear analyses from the University of Wisconsin CIMSS group suggests about 20 kt of southwesterly shear is impacting the tropical storm. This shear appears to associated with the combination of a dislodged anticyclone and an upper tropospheric cold low located a few hundred miles east-northeast of the northern Leeward Islands.



Figure 1. Latest infrared satellite image of Tropical Storm Oscar. Image credit: NOAA

While the aforementioned low is forecast to move westward and deamplify, the upper low supporting the strong baroclinic low in which Nadine is now embedded is expected to move southeastward, effectively keeping a shearing flow over Oscar. With little change anticipated in the surrounding environment over the next few days, Oscar seems poised to have a short future. In addition to the shear, the tropical storm is forecast to encounter cooler waters in about two days. The combination of these factors should assure quick dissipation. The global models are unanimous that the low over the north Atlantic will absorb Oscar in about 48 hours. Since this low is rather strong, I see no reason not to go along with this.

While some slight intensification is possible in the short-term, the shear is forecast to increase even further beyond 24 hours.

Oscar is embedded between a well-established mid-level ridge between Bermuda and the east coast of the United States and another fragment of the Bermuda/Azores ridge located to the east. Water vapor animations and data from UW-CIMSS show a developing weakness between the two ridges, obviously attributable to the large amplitude baroclinic low impinging on Nadine. Because of this, Oscar is forecast to turn northward overnight, followed by an abrupt acceleration to the northeast as southwesterly flow increases over the storm. The global models are in good agreement on the track, and I myself have no issues with the National Hurricane Center forecast track.

5-day intensity forecast

INITIAL 10/04 0300Z 35 KT 40 MPH
12 hour 10/04 1200Z 40 KT 45 MPH
24 hour 10/05 0000Z 40 KT 45 MPH
36 hour 10/05 1200Z 35 KT 40 MPH
48 hour 10/06 0000Z 35 KT 40 MPH
72 hour 10/07 0000Z...ABSORBED BY NORTH ATLANTIC LOW

5-day track forecast



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



Eastern Pacific disturbance

A large tropical disturbance centered off the south coast of Mexico is producing disorganized showers and thunderstorms. While the system continues to experience westerly shear, convection has increased a little this evening. In addition, the GFS shows the shear relaxing over the next 48 hours. No significant development is expected in the near-term, but this system will need to be monitored as it gets farther west.

I do not think this system poses a threat to land at this point, and I expect a mainly westward motion to commence for the next few days.

Probability of development in 48 hours: 20%

2012 Atlantic hurricane season Tropical Storm Oscar

Updated: 4:34 AM GMT on October 04, 2012

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Tropical weather analysis - October 2, 2012

By: KoritheMan, 4:29 AM GMT on October 03, 2012

Nadine

The eternal Nadine continues to move across the eastern Atlantic toward the Azores (again). As of the latest NHC advisory, the following information was available on the cyclone:

Wind: 50 mph, with higher gusts
Location: 34.4°N 35.7°W
Movement: E at 9 mph
Pressure: 996 mb

There is little I can say about a storm that has lasted for 82 advisories. The cyclone appears to be gradually losing organization. Strong northwesterly shear associated with a mid- to upper-level trough to the northwest has exposed the center to the western edge of the convection, although the convection still shows some banding.



Figure 1. Latest infrared satellite image of Tropical Storm Nadine. Image credit: RAMMB Colorado State University (CSU).

Sea surface temperature analyses indicate that Nadine is over SSTs of about 22 to 23C. While this is well below the threshold generally needed for tropical storm formation, AMSU temperature data suggests that the upper troposphere remains colder than normal, which has likely assisted the cyclone in lasting longer than would normally be expected for a tropical cyclone over cold water. Indeed, this is often the case with many high-latitude storms that traverse the subtropics. Unfortunately, these events are difficult to predict, which is why we usually don't incorporate them into our intensity forecasts.

In about 48 hours, a significant increase in southwesterly shear is forecast as a very strong baroclinic zone approaches Nadine. The tropical storm is forecast to respond by quickly weakening -- no matter how baroclinic an environment is, a system possessing any semblance of a warm core cannot survive in such ambience. Concurrent with its expected northeastward movement, water temperatures will cool even further, especially beyond 24 hours, when they will fall into the sub-20C range. Consequently, Nadine is forecast to lose tropical characteristics in about 48 hours. The global models suggest the cyclone will become absorbed just after 72 hours, so a day four forecast point will not be given.

Water vapor imagery shows that a deep-layer low pressure system is amplifying to the west of the tropical cyclone. Large-scale southwesterly flow is quickly approaching Nadine, and the storm is expected to soon turn northeastward as a result. Significant acceleration is forecast throughout the next three days. The model consensus remains tightly clustered as the synoptic pattern is straightforward. There is some suggestion that Nadine may move westward around the northern side of the north Atlantic low subsequent to being absorbed by it, but it would take a miracle for it to regenerate at that point.

I am in good agreement with the National Hurricane Center forecast track.

5-day intensity forecast

INITIAL 10/03 0300Z 45 KT 50 MPH
12 hour 10/03 1200Z 45 KT 50 MPH
24 hour 10/04 0000Z 45 KT 50 MPH...APPROACHING THE AZORES
36 hour 10/04 1200Z 45 KT 50 MPH
48 hour 10/05 0000Z 40 KT 45 MPH...POST-TROPICAL/EXTRATROPICAL
72 hour 10/06 0000Z 35 KT 40 MPH...POST-TROPICAL/EXTRATROPICAL
96 hour 10/07 0000Z...ABSORBED BY NORTH ATLANTIC LOW

5-day track forecast



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



Invest 96L

A vigorous tropical wave in the eastern Atlantic about 950 miles west of the Cape Verde Islands continues to show signs of organization. UW-CIMSS analysis suggests that an upper-level anticyclone is building over the disturbance, although earlier microwave data indicated that the circulation is not real well-defined. While the circulation seems to have become a little better defined since that time, it appears to be located along the far southern edge of the convection. Even that is hard to make out with nighttime imagery and a center that was not well-defined in the aforementioned microwave images.

Environmental conditions appear favorable for additional organization, and this system could become a tropical depression over the next day or two as it moves northwestward at 10 to 15 mph. Model guidance suggests this system will recurve well east of the Lesser Antilles due to the large-amplitude trough recurving Nadine. A weaker system would probably head more west and possibly threaten the northern Leeward Islands in the long-range. This appears unlikely given the current organization of the system and the favorable upper-level winds ahead of it.

Probability of development in 48 hours: 80%

2012 Atlantic hurricane season Tropical Storm Nadine Invest 96L

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Tropical weather analysis - October 1, 2012

By: KoritheMan, 12:51 AM GMT on October 02, 2012

Nadine

Nadine has weakened back to a tropical storm again. As of the latest NHC advisory, the following information was available on the storm:

Wind: 65 mph, with higher gusts
Location: 34.8°N 39.1°W
Movement: SSE at 9 mph
Pressure: 995 mb

Deep convection is limited to a band in the northern semicircle. The southern half of the circulation appears to have entrained some drier air.



Figure 1. Latest infrared satellite image of Tropical Storm Nadine. Image credit: RAMMB Colorado State University (CSU).

Nadine appears to be getting impacted by northwesterly shear, as evidenced by high cloud vectors on satellite images. A further increase in shear is forecast as the upper flow turns more northerly. In about 72 hours, an increase in southwesterly shear is forecast to impact Nadine. Assuming it has not dissipated by that time, that should surely deal the coup de grace. Nadine is expected to move across very cold water beyond 36 hours. It is possible that Nadine could become extratropical sooner than indicated below. Most of the global models show the circulation getting absorbed into a large low pressure amplifying off the eastern United States in the 72-96 timeframe.

Nadine is located between a deep-layer trough amplifying to the west, and a strong ridge to the east. This combination is expected to cause the tropical storm to turn eastward soon, followed by northeastward and then north. The models are in excellent agreement on the track, and it finally appears that Nadine has plans to exit the stage.

5-day intensity forecast

INITIAL 10/01 2100Z 55 KT 65 MPH
12 hour 10/02 0600Z 50 KT 60 MPH
24 hour 10/02 1800Z 45 KT 50 MPH
36 hour 10/03 0600Z 40 KT 45 MPH
48 hour 10/03 1800Z 40 KT 45 MPH
72 hour 10/04 1800Z 40 KT 45 MPH...POST-TROPICAL/EXTRATROPICAL
96 hour 10/05 1800Z...ABSORBED BY NORTH ATLANTIC LOW

5-day track forecast



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



Invest 96L

A vigorous tropical wave in the eastern Atlantic is centered about 750 miles southwest of the Cape Verde Islands. Data from UW-CIMSS suggest that an anticyclone is beginning to build over the disturbance, which suggests an upper tropospheric wind pattern that is conducive to intensification. Indeed, the GFS shows a very favorable environment ahead of the system for the next few days. Beyond that time, there is some dichotomy between the GFS and the SHIPS beyond the 72 hour point; the former shows 96L abruptly losing its upper support as southwesterly shear increases, while the latter shows a very favorable environment and makes the system a major hurricane in 120 hours. This was as of 18z; I am still waiting for the 0z run, which should be out momentarily.

Environmental conditions favor the formation of a tropical depression over the next day or two as the wave moves west-northwest at 15 to 20 mph.

Probability of development in 48 hours: 60%

2012 Atlantic hurricane season Tropical Storm Nadine Invest 96L

Updated: 12:55 AM GMT on October 02, 2012

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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.