VA Beach Summer Symposium - Hurricane Dynamics

Bill SammlerWarning Coordination Meteorologist

National Weather Service – Wakefield, VA

VA Beach Summer Symposium - Hurricane

DynamicsWinds, Storm Surge and

Rainfall

Let’s Start with Rainfall

Track

Tropical Cyclone RainfallHurricane Irene – 2011 vs. Floyd - 1999

Track

Tropical Cyclone RainfallHurricane Irene – 2011 vs. Isabel - 2003

The Anatomy of the post-Matthew

Flood

Overview• Third Significant Rainfall

Event in 6 weeks• Interaction with Cold Front

Enhanced Winds near the coast (SE VA/NE NC)– Matthew Not Truly Tropical

• Storm Surge/Beach Erosion a Problem

• Track Forecasts Were As Not Helpful in Assessing Potential Impacts As They Normally Are

Hurricane Matthew Track

Hurricane Matthew Rainfall

Track

Salient Points• Widespread Major Floods

Rarely Result from a Single Heavy Rain Event

• Antecedent Moisture Conditions Play a Critical Role

• Heavy Rainfall in September Made Matthew’s Flooding Possible

• Rainfall Pattern Resulted in Unusual Impacts

September Rainfall

Hurricane Matthew Rainfall

Where Does the Water Go?

Max Rainfall September through Matthew

River Graph – Lawrenceville VA

Lawrenceville, VA -9/15 to 10/18

~2 ft.

~+20 ft.

~3 ft.~4 ft.

River Graph – Franklin VA

Franklin, VA - 9/15 to 10/18

~+6 ft.

~+13 ft.

~1.0 ft.

~3.5 ft.

Tidal vs. River Graphs

Tidal vs. River Graphs

Tidal vs. River GraphsSouth Mills, NC - 9/15 to 10/18

“Record” Stage

6 Days above

“record” stage!!

~6.5 ft.

~7.5 ft.

Storm Surge Dynamics

Storm Surge DefinitionSTORM SURGE – The abnormal rise in water

level directly associated with the wind and pressure forces associated with a hurricane

Storm Surge Example – hurricane makes landfall at high tide

Storm Surge is highest in right forward quadrant near center as it crosses coast

Wave effects, which cause most coastal damage, are not accounted for in storm surge measurements

Storm SurgeStorm Surge Factors

• Storm Intensity and Size– Stronger = Higher Surge– Larger = Larger Area

Affected• Storm Speed

– Slower Often Means Higher Surge

• Angle to Coast at Landfall– Perpendicular Maximizes

Surge (Katrina)

Katrina and Sandy Examples

Union Beach, NJ (blog, Spleeness)Long Beach, NJ (White House photo – Sonya Hebert)

Biloxi, MS (NOAA) Biloxi, MS (NOAA)

Storm Surge

Storm Surge is highest and

Winds are greatest in the RIGHT FORWARD

QUADRANT close to where center makes landfall

Storm Surge vs. Location Relative to Storm

Storm Surge ExampleFACTOR = STORM DIRECTION

CAT 2 Max Surge

CAT 2 NE 20 mph

Storm Surge ExampleFACTOR = STORM DIRECTION

CAT 2 Max Surge

CAT 2 N 20 mph

Storm Surge ExampleFACTOR = STORM DIRECTION

CAT 2 Max Surge

CAT 2 WNW 20 mph

Hurricane Winds

Hurricane Wind Characteristics

• Strongest along the coast/over water, and near the center of well developed systems– Weaker/weakening systems have more chaotic

wind field

• Systems becoming non-tropical are the most difficult to forecast relative to winds (e.g Matthew – 2016)

• Hampton Roads has not experienced true hurricane winds in decades

Hurricane Irene (2011) Winds

Matthew Peak Gusts

Matthew plus Cold Front

Matthew only

The End!!Are There Any Additional

Questions?

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