91L a threat to develop, Bopha a threat for destruction; End of Hurricane Season 2012

By: TropicalAnalystwx13 , 2:22 AM GMT on December 01, 2012

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Yoga Berra, a famous former American Major League Baseball catcher, once stated, "It ain't over 'til it's over", and that saying definitely applies to the Atlantic hurricane season today. On the final official night of the 2012 season, the National Hurricane Center is monitoring a small area of low pressure in the central Atlantic. With a 30% chance of tropical or subtropical cyclone development for the time being, the disturbance is not terribly disorganized nor organized on geostationary imagery. The system as a whole has become slightly less organized over the past few hours with meager convection, but this is expected considering 91L, dubbed by the National Hurricane Center, is entering diurnal minimum and is embedded within a region of high vertical wind shear. As of the 0Z ATCF update, the invest contained maximum sustained winds of 30 mph and a minimum barometric pressure of 1012 millibars; it was moving north at 6 mph.


Figure 1. A visible and infrared satellite loop of Invest 91L.

Forecast for 91L
Invest 91L is currently embedded in a high wind shear environment and atop sea surface temperatures well below the 26 °C threshold needed to sustain a fully-tropical cyclone. In fact, the 0Z SHIPS analyzed nearly 60 knots of wind shear atop the disturbance's circulation. While this would typically rip a storm apart, the core of 91L is more subtropical in nature than tropical, and subtropical cyclones are more adapt to sustain high wind shear, cooler sea surface temperatures, and a more stable environment; this is why they form in areas tropical cyclones usually do not. Infrared imagery reveals 91L has a notable low-level circulation, but there is a high chance it is not closed. There have been no recent Advanced Scatterometer passes to evaluate the structure of the center of 91L. Nonetheless, as it drifts slowly northward or even meanders over the coming days, wind shear is expected to lower to near 30 knots. Sea surface temperatures are also expected to cool to values near 22 °C. The system has a relatively moist environment, with added moisture from a frontal zone to its northwest.

Even a subtropical cyclone cannot withstand sea surface temperatures below 24 °C for long periods of time. As 91L drifts slowly northward it will likely acquire a more tropical appearance but rapidly transition into an extratropical cyclone by 96 hours. All things considered, I'd give the system a Medium chance, 50%, of becoming a tropical or subtropical cyclone during the next 48 hours. As aforementioned, the National Hurricane Center gave the disturbance a Medium chance, 30%, of becoming a named cyclone during the next 48 hours. Their new probabilities will be likely be issued sometime in the morning in the form of a Special Tropical Weather Outlook.


Figure 2. A infrared satellite image of Typhoon Bopha.

Typhoon Bopha a serious threat
In the West Pacific, a basin historically proven to produce several storms in the month of December, spins Typhoon Bopha, a powerful Category 4-equivalent that poses a serious threat to land. With maximum sustained winds pegged at 135 mph, Bopha has residents across the Philippines scrambling to prepare for a potential impact on Tuesday. An interesting fact about Bopha is that its current position is pinned at 142 °E 4.7 °N. That's a meager 4.7 °N of the equator, and 1.1 °N north of its formation point! It's rare to see a storm form below 10 °N, much less 5 °N, and this makes Bopha one of the farthest-south forming tropical cyclones ever recorded in the northern hemisphere.

2012 Atlantic hurricane season comes to a close
The never-ending, deadly, destructive, and strange 2012 Atlantic hurricane season has finally come to an end. However, it will not soon be forgotten. The storm many people will remember for years to come is Superstorm Sandy, a beast of a hurricane that caused widespread destruction and fatalities from Jamaica and to Canada. However, the season as whole was destructive. Four tropical cyclones, including one Category 1 hurricane, struck the United States during the 2012 season: first Beryl, followed by Debby, Isaac, and finally Sandy. Tropical Storm Beryl was a system that became the strongest off-season tropical cyclone on record to hit the United States. While Debby was a borderline tropical depression/tropical storm at landfall on the Florida Peninsula, it is remembered for the rainfall totals well over a foot it produced across the region, as well as being the earliest fourth named storm on record. The first hurricane to make landfall in the U.S., Isaac, was relatively disorganized for much of its life. However, it brought a large storm surge to the coastline of Louisiana, devastating low-lying communities while also proving that the multi-billion system placed in New Orleans after Katrina will indeed protect the city from a minimal hurricane. But of course, Sandy, was the grand prize of the season, with a price tag of $65 billion dollars, which is likely to surpass $100 billion according to Colorado State University, and at least 125 USA deaths (at least 199 overall).

What makes the 2012 Atlantic hurricane season so strange, however, is not the number of landfalls and where they occurred, but the low number of intense storms in the deep tropics and the lack of intense hurricanes overall. While the season produced ten hurricanes, the sixth highest total in recorded history, only one of those ten, Michael, became a major hurricane—a Category 3 or higher on the Saffir–Simpson Hurricane Wind Scale. This can be attributed to the presence of unusually dry and stable air across much of the Atlantic throughout the season. And this can in turn be attributed to below average vertical instability–a measure of the difference of temperature between the lower atmosphere and the upper atmosphere–that has plagued the Atlantic basin for two years now. Despite the low number of intense storms, the 2012 season produced nineteen of them, making it the third most active on record (tied with 1887, 1995, 2010, and 2011).

Records and near-records

May 2012: Highest number of named storms in that particular month, tied with 1887.

Hurricane Chris: Farthest north forming hurricane before the month of August.

Tropical Storm Debby: 14th highest tornado-producing tropical cyclone.

August 2012: Highest number of named storms in that particular month, tied with 2004 and September 2007/2010.

Tropical Storm Florence: 2nd earliest formation of the 6th tropical storm of a particular hurricane season on record.

Tropical Storm Joyce: 2nd earliest formation of the 10th tropical storm of a particular hurricane season on record.

Hurricane Kirk: 2nd earliest formation of the 11th tropical storm of a particular hurricane season on record.

Hurricane Leslie: 2nd earliest formation of the 12th tropical storm of a particular hurricane season on record.

Hurricane Michael: 2nd earliest formation of the 13th tropical storm of a particular hurricane season on record.

Hurricane Nadine: 5th longest-lived tropical cyclone on record.

Hurricane Sandy: Largest known Atlantic hurricane on record by gale diameter.

Hurricane Sandy: Second costliest Atlantic hurricane on record.

Tropical Storm Tony: 2nd earliest formation of the 19th tropical storm of a particular hurricane season on record.

TropicalAnalystwx13

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5. WunderAlertBot (Admin)
1:35 AM GMT on December 22, 2012
TropicalAnalystwx13 has created a new entry.
4. pcola57
3:47 AM GMT on December 01, 2012
Good summary TA..Unusual season indeed..
Member Since: August 13, 2009 Posts: 13 Comments: 6770
3. Tropicsweatherpr
2:43 AM GMT on December 01, 2012
Good rundown of the season. About Bopha,before it reach the Philippines,it will go over or close to the island of Palau where around 21,000 people live. I hope they are preparing.
Member Since: April 29, 2009 Posts: 75 Comments: 14014
2. wxchaser97
2:32 AM GMT on December 01, 2012
Thanks TA, boy this year has been on heck of a year. What a way for me to start tracking tropical systems in depth.
Member Since: March 16, 2012 Posts: 127 Comments: 7927
1. MAweatherboy1
2:29 AM GMT on December 01, 2012
Thanks TA, it's been a great year!
Member Since: February 11, 2012 Posts: 82 Comments: 7614

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About TropicalAnalystwx13

Teenager. Weather aficionado. Soccer fan. Realist. Posts subject to sarcasm. Goal: National Hurricane Center.

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