Tropical Cyclone Danny and the Evolution (or lack thereof) of Predecessor Rainfall Events (PRE)

The Evolution of Predecessor Rainfall Events (PRE) with Tropical Cyclones Danny and Bill from the 2009 SeasonMichael L. Jurewicz, Sr.WFO Binghamton, NYNortheast Regional Operational WorkshopNovember 5, 2009 AR TC Tracks and PRE Locations

All AR TC Tracks All AR PPTC Tracks; with PRE centroids (colored dots)

2On the left side, are all Tropical Cyclone tracks within the AR category. On the right side, contain the tracks of the PRE-producing Tropical Cyclones only. The colored dots represent the locations of individual PRE centroids. The colors of the dots match those of their parent Tropical Cyclone tracks.

Mid-level StreamlinesRepresentative TC TracksTC RainfallPREsLL e-Ridge AxisSee insetUL JetConceptual Model: LOT PREs Ahead Of SR Or AR TCsRevised and updated from Fig. 13 of Bosart and Carr (1978)3This conceptual model shows a synoptic-scale pattern typically conducive for LOT PRE development, when a Tropical Cyclone is moving into the Southeastern U.S., from either the Atlantic or the Gulf of Mexico. Many of the important large-scale features previously discussed are present here. Namely, an upper-level jet streak well to the north, with much of the Mid-Atlantic and Northeastern states within its equatorward entrance region; a mid-level trough back to the west over the Great Lakes region; and a poleward feed of tropical moisture well away from the parent Tropical Cyclone, as indicated by the theta-e ridge axis stretching well off to the northeast.

BillBrief History of Bill HimselfBill was initially a Cape Verde tropical wave, which became a named storm on 15 August From 19-23 August, Bill attained hurricane status well off the U.S. East Coast (briefly reached Category 3)From 23-25 August, Bill transitioned to an extra-tropical system, as it recurved into the westerlies southeast of the Canadian maritime provinces Bills Approximate Path

Heavy Rainfall Event across New England Afternoon Rainfall on 22 August

Up to 7 (175 mm) rainfall Radar Loop

Water Vapor Loop

250 mb at 12z, 22 August

250 mb at 00z, 23 August

200 mb Height/Wind/PV, 14z, 22 August

200 mb Height/Wind/PV, 22z, 22 August

Height Rises / PV DestructionSurface Analysis, 18z, 22 August

Possible PRE850 mb Moisture Transport

Possible PRE700 mb Heights, 925 mb Winds/Theta-E, at 21z, 22 August

Near intersection of Bills moisture and pre-existing moist plumeParcel Trajectories into Central New England

Bills TrackBill SummaryBill fit into the AR track for potential PRE-producing systemsOne main heavy rain episode took place on the periphery of Bills influenceSouthern NH on 22 August4-7 (up to 175 mm) of rain fell within just a few hours, causing flash flooding Transient nature of heavier rain bands precluded excessive rainfall/runoff problems elsewhere

DannyBrief History of Danny HimselfDanny was initially a Cape Verde tropical wave, and took several days to become a named storm Finally, on 26 August, it attained Tropical Storm status east of the BahamasFrom 26-29 August, Danny remained a Tropical Storm well off the Southeast U.S. coastFrom 29-31 August, Danny weakened to a Tropical Depression, and ultimately transitioned to an extra-tropical system, as it recurved off the U.S. East Coast Dannys Approximate Path

Heavy Rainfall Event across the Mid-Atlantic RegionLate Night/Early Morning Rainfall, 27-28 August

4-8 (100-200 mm) rainfallRadar Loop

250 mb at 00z, 28 August

Water Vapor Loop

700 mb Heights, 925 mb Winds/Theta-E, at 05z, 28 August

Axis of tropical moistureSeparate moist axis850 mb at 00z, 28 August

Parcel Trajectories into the Mid-Atlantic Region

200 mb Height/Jet/PV, 02z, 28 August

200 mb Height/Jet/PV, 09z, 28 August

SB CAPE Analysis, 06z, 28 August

Heavy Rainfall Event Just off the Mid-Atlantic CoastLate Afternoon/Overnight Rainfall, 28-29 August

Widespread 5-10 (up to 250 mm) rainfallRadar Loop, 28-29 August

250 mb at 00z, 29 August

Water Vapor, 28-29 August

700 mb Heights, 925 mb Winds/Theta-E, at 03z, 29 August

Tropical Moisture AxisSB CAPE Analysis, 00z, 29 August

Possible PRESurface Analysis, 00z, 29 August

Possible PRE850 mb Analysis, 00z on 29 August

Parcel Trajectories into the Mid-Atlantic Coastal Region

Dannys TrackDanny SummaryDanny fit into the AR track for potential PRE-producing systemsTwo distinct heavy rain episodes took place on the periphery of Dannys influenceEvent that most resembled a PRE took place just offshore, 28-29 AugustHeavy rain/flash flooding that occurred in the Baltimore area appeared to lack sufficient moisture contributions from Danny or jet interactionsLack of a direct moisture connection with the TC, as well as a relatively cool stable air mass, seemed to protect much of the Northeastern U.S. from excessive rainfall