Tropical Storm Andrea Spreading Heavy Rains to U.S. East Coast

Tropical Storm Andrea is rapidly losing its tropical characteristics as it barrels northeastwards at 27 mph up the U.S. East Coast, but it still has plenty of tropical moisture that is feeding very heavy rains. Rains of 2 - 4" are expected along a swath from South Carolina to New England from Andrea over the next two days. Pine Ridge, NC has received 6.5" of rain from Andrea, and New River MCAS, North Carolina picked up 2" of rain as of 9 am EDT this morning, along with a wind gust of 47 mph at 3:18 am. The same band of heavy thunderstorms spawned a possible tornado near Hubert, North Carolina at 4:45 am EDT. Andrea has spawned a preliminary count of eleven tornadoes, which is a respectable number for a landfalling June tropical storm, but not a record. According to TWC's severe weather expert Dr. Greg Forbes, there have been two other June tropical storms since the year 2000 that spawned far more tornadoes--Tropical Storm Bill during June 29 - July 3, 2003 (32 tornadoes in FL, GA, LA, AL, MS, SC, NC, NJ), and Tropical Storm Allison of June 7 - 17 2001 (28 tornadoes in FL, AL, GA, LA, MS, SC, VA, MA, ME.) Only one of Andrea's tornadoes caused an injury, a tornado that hit The Acreage in Palm Beach County at 6:45 am EDT. The highest storm surge from Andrea was 4.55' at Cedar Key, Florida.


Figure 1. Yummy’s cafe in Gulfport, Florida was hit Thursday morning by a waterspout that moved ashore and became a tornado.(LAUREN CARROLL/Tampa Bay Times)


Figure 2. Predicted rainfall for the 48-hour period from 8 am EDT Friday, June 7, to 8 am EDT Sunday, June 8, 2013. Image credit: NOAA.


Video 1. NASA animation of Andrea satellite images. More cool NASA images of Andrea are here.

The Atlantic hurricane season is getting longer
Andrea's formation in June continues a pattern of an unusually large number of early-season Atlantic named storms we've seen in recent years. Climatologically, June is the second quietest month of the Atlantic hurricane season, behind November. During the period 1870 - 2012, we averaged one named storm every two years in June, and 0.7 named storms per year during May and June. In the nineteen years since the current active hurricane period began in 1995, there have been fifteen June named storms (if we include 2013's Tropical Storm Andrea.) June activity has nearly doubled since 1995, and May activity has more than doubled (there were seventeen May storms in the 75-year period 1870 - 1994, compared to 6 in the 19-year period 1995 - 2013.) Some of this difference can be attributed to observation gaps, due to the lack of satellite data before 1966. However, even during the satellite era, we have seen an increase in both early season (May - June) and late season (November - December) Atlantic tropical storms. Dr. Jim Kossin of the University of Wisconsin looked at the reasons for this in a 2008 paper titled, "Is the North Atlantic hurricane season getting longer?" He concluded that there is a "apparent tendency toward more common early- and late-season storms that correlates with warming Sea Surface Temperature but the uncertainty in these relationships is high." He found that hurricane season for both the period 1950-2007 and 1980-2007 got longer by 5 to 10 days per decade (see my blog post on the paper.)

Invest 92L in the Central Atlantic no threat to develop
Satellite images show that disorganized tropical wave is in the Central Atlantic, about a two-day journey from the Lesser Antilles Islands. NHC designated this system 92L Thursday afternoon. High wind shear of 30 - 40 knots is ripping up the thunderstorms in 92L as they form, and wind shear is predicted to remain 30 - 40 knots for the next five days, making development unlikely. The wave will likely bring heavy rain showers and gusty winds to the northern Lesser Antilles Islands beginning on Sunday night. None of the reliable computer models is showing development of a tropical cyclone in the Atlantic over the next seven days.

Jeff Masters