An Examination of the Tropical System – Induced Flooding in Central New York and Northeast Pennsylvania in 2004 Tropical Systems Produced Major Flooding in Central New York and Northeast Pennsylvania in 2004 Remains of “Bonnie” – Flash flooding in the western Catskills. Remains of “Gaston” – Flash flooding in the Finger Lakes and Syracuse area. Remains of “Frances” – Flash Flooding in south central NY. Remains of “Ivan” – Major Flooding in southern New York and northeast Pa. Outline A brief review of previous research on enhanced precipitation in the northeast associated with tropical storms transitioning to extra-tropical. A brief overview of each storm, including the large- scale flow and precipitation pattern associated with each storm, as well as each storm’s effects on central NY / northeast Pa. A little more on two of these storms, with emphasis on findings from previous research. Summary. Heavy rain is especially enhanced when enhanced low-level inflow interacts with coastal fronts and/or terrain. Topographical map of the New York, Pennsylvania and Western New England. Tropical Storm Bonnie Tropical storm Bonnie moved north across the Gulf of Mexico to northern Florida on August 12. Moisture “associated with” Bonnie produced significant flash flooding in the western Catskill mountains and northeast Pocono mountains on the 12th. Surface plot August 12, 2004 20 UTC. GFS 00-hr 300 mb hts and wind speed August 12, 18 UTC. August 12, 2004 16 UTC August 12, 2004 20 UTC. Radar estimated rainfall through 00 UTC August 13. Tropical Storm Gaston Tropical Storm Gaston moved north across the southern Atlantic, making landfall in South Carolina on the 29th. The storm weakened to a depression, then re-strengthened to a tropical storm as it moved north off the Delmarva peninsula on the 30th. Significant flash flooding occurred on the 30th in the Finger Lakes and Syracuse area. Surface plot August 30, 2004 21 UTC. 00-hr GFS 300 mb heights and wind speed August 30, 18 UTC. August 30, 2004 12 UTC. August 30, 2004 20 UTC. Radar estimated rainfall through 00 UTC August 31st. Hurricane Frances The remains of Hurricane Frances moved north from the Gulf of Mexico up the west slopes of the Appalachians on the 8th. The surface low pressure center tracked from southwest Pennsylvania north to western New York during the morning on the 9th. Flooding in central New York was confined to the central southern tier (much more farther west and south). Surface plot September 9, 2004 12 UTC. GFS 00-hr 300 mb heights and vorticity September 9, 06 UTC. September 9, 2004 04 UTC. September 9, 2004 08 UTC. Radar estimated rainfall through 2049 UTC, September 9. Hurricane Ivan The remains of Hurricane Ivan moved northeast from the central Gulf Coast, reaching northern Virginia early on the 18th. Widespread 4 to 7 inch rainfalls over northern Pennsylvania and southern New York brought major flooding to a wide area. Surface plot September 18, 2004 06 UTC. GFS 00-hr 300 mb heights and wind speed September 18, 00 UTC. September 17, 2004 21 UTC. September 18, 2004 03 UTC. Radar estimated storm total precipitation through September 18, 2004 18 UTC. CSTAR research on precipitation and tropical cyclones in New England indicates precipitation is maximized when… Upper-level anticyclonic outflow results in an enhanced upper-level jet northwest-northeast of the surface cyclone. The right entrance region of the upper-level jet is located over the potential heavy rain area. Enhanced low-level jet develops along with enhanced θe advection. Precipitation is frequently enhanced by interactions between the low-level jet and coastal fronts / topography. Factors Favorable For Warm Season / Convective Flash Flooding Strong low-level jet (>30 (20) kts) / θe advection. Weak mid-level winds / weak mid-level shear. Deep warm cloud layer (greater than 3 km). Moderate – high “skinny” CAPE south of the heavy rain (NCAPE < 0.10). Precipitable Water > 130 percent of normal. Weak short-wave trof upstream of heavy rain. Upper-level divergence / jet entrance region. In our 4 cases, there appeared to be two distinct types… Heavy convective rains developing well to the north of the tropical cyclone (Bonnie and Gaston). Heavy rains more directly associated with the transitioning tropical cyclone (Frances and Ivan). Let’s look at a representative case from each type in a little more detail. Tropical Storm Gaston Representative of the cases where flash flooding developed associated with convection well to the north of the primary surface low. Surface front 6-hr Eta forecast vertical circulation, divergence and wind speed (shaded) valid 18 UTC August 30st. flooding Eta 6-hr forecast vertical circulation, frontogenesis and negative EPV (shaded blue) valid August 30, 18 UTC. Eta 6-hr 925 mb theta-e advection and wind August 30, 18 UTC. Eta 6-hr lifted index and 3-6 km bulk shear August 30, 18 UTC. Eta 9-hr BUFKIT sounding at ELM valid August 30, 21 UTC. 20 kt low-level jet Eta BUFKIT Time-section of wind at IPT Gaston - Summary Pronounced upper-level jet entrance region coupled with a low-level front. Moderate, surface-based instability. Weak low-level Өe advection (20 kt low-level jet), separate from flow associated with Gaston. Mid-level shear (3-6 km) around 10 kts. Warm cloud depth around 3 km. Precipitable water around 1.6 inches. Heaviest rain in the hilly terrain of northern Oneida county southwest to the southern edge of the Syracuse area. Ivan Representative of the cases with more widespread heavy rain associated more directly with a tropical cyclone. The worst flooding in our county warning area since 1996. Deep frontal zone Eta 6-hr vertical circulation, divergence and wind speed September 18, 06 UTC. flooding Eta 6-hr vertical circulation, frontogenesis and negative EPV September 18, 06 UTC. Eta 6-hr 850 mb theta-e advection and wind September 18, 06 UTC. Eta 6-hr lifted index and 3-6 km bulk shear September 18, 06 UTC. Eta 6-hr BUFKIT sounding at IPT valid September 18, 06 UTC. Low-level jet Eta BUFKIT time section of wind speed at IPT Eta BUFKIT elevated CAPE at IPT Summary - Ivan Pronounced upper-level jet entrance area coupled with a low-level front. Deep, sloping area of frontogenesis. Instability mainly located at mid-levels around 700 mb. Strong low-level Өe advection (40 kt low-level jet). Strong instability gradient – mid-level (3-6 km) shear 10 to 20 kts. Warm cloud depth around 4 km. Precipitable water around 1.9 inches. Heaviest rain in northern Pennsylvania – no obvious, strong topographic influence. Summary Two distinct patterns were identified that were associated with flooding. Both types had much in common, and much in common with other flood events studied previously.