Presentation on theme: "Tropical Cyclone Hazards in the Pacific"— Presentation transcript:
1 Tropical Cyclone Hazards in the Pacific Robert A. BallardCentral Pacific Hurricane CenterHonolulu, HI
2 Briefing Outline What is a tropical cyclone? Tropical cyclone ingredientsTropical cyclone climatologyTropical cyclone impacts
3 What is a Tropical Cyclone? A low pressure area that is warmer on the inside than on the outside – i.e., warm coreCan be dozens to hundreds of miles wide, and last for daysNo fronts attached; i.e., no fronts through low centerForms over warm tropical or subtropical oceansProduces organized thunderstorm activityHas a closed surface wind circulation around a well-defined centerClassified by maximum sustained surface wind speedTropical depression: < 39 mphTropical storm: mphHurricane/Typhoon: 74 mph or greater
4 Tropical Cyclone Ingredients Sea Surface Temperatures usually above 26.5°C (80°F) over a large areaLow level disturbance in the wind fieldDeep moistureInstabilityWeak vertical wind shear (winds slowly changing with height)Distance from the equator
6 Tropical Cyclone climatology average: 31average:4-5average: 6average: 28Western North Pacific is the most active Tropical Cyclone basin in the worldCan’t be too focused on total number or forecast number for the season!“It only takes one.”
9 Tropical Cyclone Impacts Extreme WindsCan last from an hour or two, to a day or more, depending on how fast the tropical cyclone is moving.Can affect a relatively small area, or a relatively large swath, depending on the size of the tropical cyclone.Possible to build structures to withstand the winds, but flying debris can still cause damage & kill.Terrain effects can locally accelerate winds.
10 Tropical Cyclone Impacts Intense RainfallResults in catastrophic flash flooding.Several months’ worth of rainfall can fall in a 24 hour period.Is not dependent on the strength of the tropical cyclone.Even weak or dissipated tropical cyclones can bring catastrophic rainfall.Any slow moving system brings the largest threat.Can result in numerous rockslides & landslides.Blocks roadsFailure of structures built on hillsides.Rain often can’t escape to the ocean because of storm surge flooding.
11 Tropical Cyclone Impacts Storm surgeAbnormal rise of water level generated by a storm, well above the predicted astronomical tide.Temporary rise in sea level effectively moves the coast well inland.Structures near the shore are inundated.Storm surge + wave runup + astronomical tide + freshwater flooding = “total water level”Greatest potential killer in a tropical cyclone!
12 Tropical Cyclone Impacts TornadoesFriction of extreme winds interacting with land can cause sudden tornado spinups.Most common to the right of the track of the tropical cyclone.Usually fast moving, brief, and hard to issue warnings for.Can cause areas of enhanced damage above & beyond that expected from the tropical cyclone itself.Can occur even well away from the center in the outer rain bands.
13 ConclusionTropical cyclones present a complex variety of weather & water hazards.Tropical cyclones are often not well understood. They require a considerable amount of education before & during an event.Preparation & planning can help mitigate losses.