The North Wall Picture Source The Perfect Storm

The North Wall…. Picture Source: “The Perfect Storm”

NORTH WALL EFFECT Cold Air Flow AT: 21 o. F Land 53 o. F Cold Water Extreme Winds & Seas North Wall 2 NM 75 o. F Gulf Stream

North Wall Effect Ø Typically a cold season event o Creates high, steep seas, in and near the Gulf Stream o Effects usually confined to a small area o Quick to develop (Explosive) o Two types • Perpendicular flow (NW) • Opposing flow (NE) Rogue wave estimated at 60 feet moving away from ship after crashing into it a short time earlier. In the Gulf Stream off of Charleston, South Carolina, with light winds of 15 knots.

Perpendicular flow o Cold Air Flows Over Warm Water – minimum 20 degrees (F) temperature difference required – common with cold air outbreaks over central Atlantic coast o Dramatic temperature gradient in the vicinity of the Gulf Stream results in – higher winds speeds on and near surface o Higher Surface Winds = Higher Waves o Worst area is where Gulf Stream is closest to land (i. e. Hatteras)

PERPENDICULAR WIND FLOW Air Temp: 45 Deg SFC Winds: 30 kts Max Winds 45 kts Gusts to 60 kts North Wall Hatteras eam Gulf Str South Wall V 3 s Ts 5 -7 20 ft 15 ft • Air is less modified and features extreme gustiness • Effects felt further seaward • Often occurs with explosive cyclogenesis

OPPOSING WIND FLOW Ø Northeast winds flowing over a northeastward moving current Ø Generates very high, steep waves over a fairly narrow zone Ø Temperate contrast not as important Ø Typically occurs with a stalled front off the mid-Atlantic coast, or nearly stationary Newfoundland Low Ø Common with developing “Hatteras” storm force low The mast visible on the starboard side is 25 m above sea level, and the wave is breaking from behind the ship. The wave was at least 20 m high, perhaps 30 m (since its trough, as well as crest, would be lower than other waves).

Air Temp: 45 Deg SFC Winds: 30 kts OPPOSING WIND FLOW Max Winds 40 kts Gusts to 55 kts North Wall 15 ft Hatteras 15 15 32 Gulf Stream 20 South Wall 22 3 s V Ts 5 -7 15 15 • Wind fetch opposes Gulf Stream • Narrow zone established with steeper waves • Not dependent on season