Preliminary Report
Tropical Storm Helene
15 - 25 September 2000

2000 PRELIMINARY REPORTS

Hurricane Alberto (3)
Tropical Storm Beryl (TS)
Tropical Storm Chris (TS)
Hurricane Debby (1)
Tropical Storm Ernesto (TS)
Hurricane Florence (1)
Hurricane Gordon (1)
Tropical Storm Helene (TS)
Hurricane Isaac (4)
Hurricane Joyce (1)
Hurricane Keith (4)
Tropical Storm Leslie (TS)
Hurricane Michael (2)
Tropical Storm Nadine (TS)

Helene made landfall as a minimal tropical storm near Fort Walton Beach, Florida and redeveloped into a strong tropical storm over the North Atlantic.

 

a. Synoptic History

Helene developed from a tropical wave that emerged from the African coast on 10 September. The wave lost all of its deep convection the next day as it continued moving westward. There was little sign of redevelopment until 14 September when convection formed near the center of the system. Showers and thunderstorms continued overnight and Dvorak satellite estimates indicate that Tropical Depression Twelve formed on the afternoon of the 15th. The depression appeared to weaken before aircraft reconnaissance first flew into the system the next day. The aircraft could not find a closed circulation, indicating that the depression had degenerated into a tropical wave. It is notable that, even without any center, the plane reported winds in excess of 63 mph at 1500 ft to the north and east of the wave.

The remnants of the depression moved over the Leeward Islands on the 17th, producing heavy rains and gusty winds to tropical storm force in squalls. Upper-level conditions seemed very favorable for regeneration, but the system was slow to redevelop. It was not until late on the 19th that a reconnaissance aircraft found a closed circulation northwest of Grand Cayman Island, while the system was moving more to the west-northwest. The depression was very weak with only a few thunderstorms near the center when it crossed the western tip of Cuba the next day. However, convection redeveloped near the center and it became Tropical Storm Helene early on the morning of the 21st in the southeast Gulf of Mexico. The storm moved northwestward, strengthening under marginally favorable conditions. However, the vertical wind shear increased, preventing Helene from attaining hurricane status. The system became very asymmetric as a result of the shear, with most of its deep convection, winds, and heavy rainfall displaced to the east of the center. It peaked at a maximum intensity of 69 mph about twelve hours before landfall. The shear increased further and weakened Helene to an intensity of 40 mph during landfall near Fort Walton Beach, Florida around 7 am CDT on the 22nd. Helene then moved toward the northeast over the southeastern states as a tropical depression.

Even with strong westerly shear, deep convection began to intensify over the coastal waters of North Carolina when the system approached the east coast. Tropical storm force winds were measured at stations off the coast of North Carolina. A post-analysis of buoy data and satellite imagery indicates that Helene had developed enough tropical characteristics to be considered a tropical cyclone as it emerged from the coast of Virginia. The cyclone began to race northeastward away from the United States toward decreasing shear. Ship observations and satellite images indicate the system was very compact over the Atlantic, no more than 120 nautical miles wide with the strongest winds in the south and east quadrants. An intense burst of convection formed over the center on the 24th, and it is estimated that Helene reached a second peak intensity of 69 mph early on the 25th before merging with a cold front later that day.

b. Meteorological Statistics

The intensity or redevelopment of Helene as it emerged off the Mid-Atlantic coast would likely never have been known if not for the hourly reports of the ship Neptune Olivine. The ship reported sustained winds of 64 mph at 0600 UTC on the 25th as the storm moved nearby. An intensity of 69 mph has been estimated from this ship report. The ship also recorded a lowest pressure of 988.2 mb with a westerly wind of 53 mph. However, it is likely that the ship did not report the minimum pressure as the winds indicate that the ship was displaced to the south of the center and a final estimate of 986 mb has been made. It is notable that Neptune Olivine had reports that were similar to another ship to its southeast, the Global Mariner, that reported sustained winds of 60 mph at the same time that the Neptune Olivine reported 64 mph.

1. Rainfall Data

The storm caused extensive flooding in Tallahassee, Florida where it dumped near nine inches of rain.

c. Casualty and Damage Statistics

There was 1 death attributed to Helene; 1 in South Carolina.

The one casualty associated with Helene was a man killed in a F2 tornado in South Carolina as the tropical depression moved through the region on the 23rd.