Predecessor Rain Events: A Literature Review By: Tony Viramontez
Introduction Predecessor Rain Event (PRE): meso- and subsynopticscale regions of high-impact heavy rainfall that occur well in advance of recurving tropical cyclones (TCs)
Requirements Coherent region of rainfall rainfall > 100 mm (approx. 4 in) in 24 hr Typically, positioned 1000 km poleward and separate from TC initiates 36 hr prior to the arrival of the TC
Requirements Tropical Moisture Precipitable water values > 50 mm Associated with TC and advected poleward by TC Occurs where deep tropical moisture intersects region of forced ascent Beneath an equatorward jet- entrance region. Frontal or Orographic Shortwave
Idealized Synoptic Scale environment of a left of TC track (LOT) PRE. (From Moore (2010))
Why do we care? Forecasting Challenges Models do not handle PRE s well Difficulty representing TC and mid-latitude interactions While focus is on TC, PRE s can catch forecasters by surprise Societal Impacts Flooding
Societal Impacts Base reflectivity mosaic from 1200 UTC 8 Sep 2004 of TC Frances and a front page photo and article highlighting the flooding from the high-impact TC Frances PRE (2004, The New York Times). (From Galarneau 2010)
Where? Eastern 1/3 of the U.S. Approximately 30% of all TCs that pass west of 70 W and north of 20 N (near Dominican Republic/Haiti) produce a PRE Southwestern U.S. Eastern Asia Satellite Imagery of Typhoon Songda (2004) from Wang et al. 2009.
When? Histogram of the monthly frequency distribution of all TCs (gray bars) and TCs that produced PREs (black bars) during 1995 2008. (From Moore 2010) Earliest documented PRE occurred in the Northeast U.S in 1938
How Intense is the Parent TC? Maximum TC intensity on the Saffir Simpson scale category for all TCs (gray bars), TCs that produced PREs (black bars), and the TC intensity at the time of PRE initiation (clear bars) during 1995 2008. (From Moore 2010)
Categories Categories based on large scale synoptic flow pattern 1) Upper Level Jet Structure Upper-level ridge ( anticyclonically curved category) Upper-level trough ( cyclonically curved category) 2) Further classifications account for variations beyond simply trough or ridge Downstream Confluent Southwesterly Jet Jet in Ridge
Downstream Confluence An upper-level trough is situated downstream and poleward of the TC, and the jet streak is positioned in a region of confluence downstream of the TC. Geopotential height contours are shown in black, the jet streak is represented by the gray shaded region, and the location of maximum wind speed is denoted by the J symbol. PRE and TC locations are indicated by the + symbol and the tropical storm symbol, respectively. (From Moore 2012)
PRE initiation locations (green) from 1988-2010 and the TC locations (red) at the time of PRE initiation. (From Moore 2012) Idealized synopticscale environment for southwesterly jet PRE s. (From Moore 2012)
Southwesterly Jet Features a southwesterly jet streak positioned downstream of an upper-level trough that is located immediately upstream and poleward of the TC. Same as before. (From Moore 2012)
Idealized synoptic-scale environment for southwesterly jet PRE s. (From Moore 2012)
Same as above. Due to number of examples, the plots were split. (From Moore 2012) PRE initiation locations (green) from 1988-2010 and the TC locations (red) at the time of PRE initiation. From Moore 2012)
Jet in Ridge Features an anticyclonically curved jet streak on the poleward flank of a broad upper-level ridge, with the TC beneath Occur exclusively in the Midwest Same as before. (From Moore 2012)
PRE initiation locations (green) from 1988-2010 and the TC locations (red) at the time of PRE initiation. (From Moore 2012) Idealized synoptic-scale environment for jet in ridge PRE s. (From Moore 2012)
Total precipitation (mm) for Typhoon Songda between 1800 UTC 2 Sep and 0000 UTC 5 Sep 2004 in (a) the control experiment and (b) the No- Typhoon experiment run with the Advanced Research WRF model. (From Wang 2009)
Ernesto (2006) 8/24 9/04 Maximum Wind Speed: 75 mph Lowest Central Pressure: 985 mb Downstream confluent, anticyclonically curved jet (From Weather Underground)
Precipitable Water (PW) Precipitable water is a measure of the depth of liquid water at the surface that would result after precipitating all of the water vapor in a vertical column over a given location, usually extending from the surface to 300mb.
54 mm = 2.13 in 53 mm = 2.09 in Soundings for a) Greensboro, North Carolina and b) Newport, North Carolina. (From Moore 2010)
Precipitable Water Values for 1800 UTC 30 August 2006. (From Moore 2010)
2.09 in Newport, North Carolina Precipitable Water Climatology (from NWS)
Impact of TC Ernesto Maximum Rainfall Amount (including PRE and TC): 14.61 at Wrightsville Beach, North Carolina Maximum Rainfall Amount from PRE: 9.85 at Grifton, North Carolina Flooding was the primary impact of Ernesto Costliest Storm of the 2006 Atlantic Hurricane Season (Cost = $500 million (US dollars)
Charley (2004) 8/09 8/15 Maximum Wind Speed: 145 mph Lowest Central Pressure: 947 mb Southwesterly jet, cyclonically curved jet (From Weather Underground)
Sounding for Jacksonville, Florida 65.38 mm = 2.57 in
2.57 in Jacksonville, Florida Precipitable Water Climatology (From NWS)
Impacts of Charley Maximum Rainfall Amount from TC and PRE: 9.88 at Bud Slough, Florida. Cost: >$15 billion (US dollars)
TC Rita (2005) 9/18 9/26 Maximum Wind Speed: 180 mph Lowest Central Pressure: 897 mb One of the most intense Atlantic Hurricanes ever Jet in ridge, anticyclonically curved jet (From Weather Underground)
Surface
36 mm = 1.42 in 37 mm = 1.46 in Soundings for a) Omaha, Nebraska and b) Chanhassen, Minnesota. (From Moore 2010)
Precipitable Water Values for 0000 UTC 25 September 2005. (Moore 2010)
1.42 in Omaha, Nebraska Precipitable Water Climatology (From NWS)
Impact of Hurricane Rita Maximum Rainfall Amount from TC: 16.00 at Bunkie, Louisiana Maximum Rainfall Amount from PRE: 7.8 Cost: >$12 billion (US dollars)
Summary Predecessor Rain Events (PREs) are a coherent region of heavy rainfall associated with deep tropical moisture advected poleward by a TC 3 Categories: Downstream confluence, southwesterly jet, and jet in ridge PREs have a large human impact potential through heavy rainfall and flooding.
References Bosart, L. F., J. M. Cordeira, T. J. Galarneau, B. J. Moore, H. M. Archambault, 2012: An analysis of multiple predecessor rain events ahead of tropical cyclones Ike and Lowell: 10 15 September 2008. Mon. Wea. Rev., 140, 1081 1107. Cote, M. R., 2007: Predecessor rain events in advance of tropical cyclones. M.S. thesis, Department of Atmospheric and Environmental Sciences, University at Albany, State University of New York, 200 pp. [Available online at http://cstar.cestm.albany.edu/cap_projects/project10/index.htm.] Galarneau, T. J., L. F. Bosart, R. S. Schumacher, 2010: Predecessor rain events ahead of tropical cyclones. Mon. Wea. Rev., 138, 3272 3297. Moore, B.J., 2010: Synoptic-scale environments and dynamical mechanisms associated with predecessor rain events ahead of tropical cyclones. Thesis, Department of Atmospheric and Environmental Sciences, University at Albany, 150. Moore, B. J., L. F. Bosart, D. Keyser, M. L. Jurewicz, 2013: Synoptic-scale environments of predecessor rain events occurring east of the rocky mountains in association with Atlantic basin tropical cyclones*. Mon. Wea. Rev., 141, 1022 1047. Schumacher, R. S., T. J. Galarneau, L. F. Bosart, 2011: Distant effects of a recurving tropical cyclone on rainfall in a midlatitude convective system: A high-impact predecessor rain event*. Mon. Wea. Rev., 139, 650 667. Schumacher, R. S., T. J. Galarneau, 2012: Moisture transport into midlatitudes ahead of recurving tropical cyclones and its relevance in two predecessor rain events. Mon. Wea. Rev., 140, 1810 1827. Wang, Y., Y. Wang, and H. Fudeyasu, 2009: The role of Typhoon Songda (2004) in producing distantly located heavy rainfall in Japan. Mon. Wea. Rev., 137, 3699 3716.