ANOTHER BUSY TROPICAL SEASON?

 

By Jim Hudgins and Ken Kostura

 

 

After a very active tropical summer of 2004, preliminary indications show that another slightly above average tropical cyclone season may be in store. Also, an above average probability of U.S. major landfalls is anticipated. However these numbers of U.S. landfalling systems is expected to be well below that of 2004. Specifically, it is estimated that 2005 will have about 6 hurricanes (average is 5.9), 11 named storms (average is 9.6), and 3 intense (category 3-4-5) hurricanes (average is 2.3). The probability of U.S. major hurricane landfall is forecast to be 30 percent above the long-period average, which is computed between 1950 and 2000.

 

The list of names for the upcoming 2005 Atlantic Hurricane season includes: Arlene, Bret, Cindy, Dennis, Emily, Franklin, Gert, Harvey, Irene, Jose, Katrina, Lee, Marian, Nate, Ophelia, Philippe, Rita, Stan, Tammy, Vince, and Wilma.

 

Tropical cyclones that move inland across the region can produce problems ranging from catastrophic amounts of rain to tornadoes as well as straight-line wind damage. Typically August and September are most apt to see effects from tropical cyclones (Fig 1), although the early summer and fall months can see a few storms as well.

 

 

Graph of Hurricane distribution by Month

 

Fig 1. Graph depicting monthly distribution of storms passing

within 300 miles of Blacksburg VA since 1950.

 

The mountainous regions of the Blue Ridge and Central Appalachians usually are the focus for flooding rainfall, while tornadic activity is most common in the piedmont and foothills. However, in general fast moving stronger storms that move inland from the Carolinas can produce significant wind damage throughout the area.

 

The different tracks along with intensity and location of landfall bring different weather impacts. These tracks range from systems passing west of the mountains, overhead the region, or to the east. Those tracking to the west typically have the least impact with those going directly overhead the most. Variations in impact can be significant depending on strength at landfall, speed of movement, and interactions with other weather features.

 

Systems that move overhead (Fig 2) tend to produce the most flooding and wind problems especially those that pass inland off the Atlantic Ocean. In these cases, southeast winds (upslope flow) tend to enhance rainfall across the eastern slopes of the Blue Ridge and promote tornadic producing rainbands over the piedmont.

 

 

Track of Hurricane IvanRainfall map of Hurricane Ivan

 

Fig 2. Example of Overhead Track

Including Rainfall Totals

(Ivan 2004).

 

Those storms that slide east (Fig 3) of the region (through eastern VA or NC) provide for heavy rain but are highly dependent on strength and size of the system. They also can produce strong winds but generally few tornadoes.

 

 

Track of Hurricane Agnus Rainfall from Hurricane Agnus

 

Fig 3. Example of Track East of the

Mountains Including Rainfall Totals

(Agnes 1972).

Rainfall and wind effects are usually much less with cyclones (or their remnants) moving west (Fig 4) of the Appalachians. These are for the most part Gulf Coast land falling systems that have lost much of their intensity via their longer track over land. Although Camille in August 1969 was an exception in which the system crossed the mountains from the west and was enhanced by an old frontal boundary along the Blue Ridge.

 

 

Track of Hurricane Opal Rainfall from Hurricane Opal

 

Fig 4. Example of Track West of the

Mountains Including Rainfall Totals

(Opal 1995).