Hurricane Harvey's Tornadoes: Challenges for Forecasting and Communication Roger Edwards and Jeff Evans SPC Norman OK, and NWS WFO Houston/Galveston, Texas
HARVEY TORNADOES HIT HOUSTON
GENERAL FACTS: TC TORNADOES MOST COMMON IN <50-kt (tropical storm or weaker) WIND AREA MOST COMMON NNW-NE-SE OF CENTER MOSTLY WEAK (EF0-EF1), RARELY EF3-4 CAN OCCUR FAR INLAND for SEVERAL DAYS MOST COMMON AND DAMAGING FROM MIDDLE-OUTER SUPERCELLS (EF0-EF3, TWO F4S SINCE 1950) MORE COMMON in DAYTIME OCCUR OVER WATER AND CAN MOVE ASHORE OCCUR IN EVERY STAGE OF CLASSIFICATION DETAILED DISCUSSION IN EDWARDS (2012), EJSSM
TC TORNADO FACTS & CLIMATOLOGY Geography of 1313 TCTOR events 1995-2016
TC TORNADO FACTS & CLIMATOLOGY TCTOR DATA: TC STRENGTH AT TORNADO TIME (from Hurricane Database)
TC TORNADO FACTS & CLIMATOLOGY Highly variable year-to-year in WSR-88D era
TC TORNADO FACTS & CLIMATOLOGY Doppler radar era: Many more weak TC tornado reports, many more TC tornado reports PERIOD! data from Schultz and Cecil (2009) and TCTOR
TC TORNADO FACTS & CLIMATOLOGY DAMAGE RATINGS PERCENT by EF RATING
TC TORNADO FACTS & CLIMATOLOGY DAYTIME FAVORED In deep moist environment, even subtle warming under cloud cover or in clear slots greatly increases instability. Harvey s 52 total tornadoes skewed toward morning
TC TORNADO FACTS & CLIMATOLOGY ALL TCs H Tornadoes more common in SE sectors as TCs weaken WHY? TS TD and Unc. That sector s over water in most mature hurricanes!
TC TORNADO FORECASTING CONCEPTS INGREDIENTS-BASED THINKING VALID WHETHER MIDLATITUDE OR TROPICAL! MOISTURE: usually no problem!!! INSTABILITY: daytime heating offsets weak instability aloft LIFT: Spiral bands, embedded boundaries, FREQUENT ANALYSIS is CRUCIAL! VERTICAL SHEAR: Max in favored N NE - SSE sector Edwards 2012
SPC FORECASTS for HARVEY Day-4 8 Outlooks
SPC FORECASTS for HARVEY Day-3 Outlooks
SPC FORECASTS for HARVEY Day-2 Outlooks
SPC FORECASTS for HARVEY Day-1 Outlooks
SPC FORECASTS for HARVEY CITY of HOUSTON: 60 HOURS in TORNADO WATCHES WFO WARNING AREA: 96 HOURS!
PRELIMINARY TORNADO MAP: HARVEY (25 31 AUGUST 2017)
HARVEY vs. ALL-TIME LEADERS TROPICAL CYCLONE YEAR TORNADO REPORTS ALL- TIME TOP-10 LIST H Ivan 2004 118 H Beulah 1967 115 H Frances 2004 103 H Rita 2005 98 H Katrina 2005 59 H Andrew 1992 56 TS Fay 2008 50 H Gustav 2008 49 H Cindy 2005 48 H Georges 1998 48 From TCTOR and pre-1995 formal studies H Harvey 2017 52
Hurricane Harvey: The greatest rainfall from a U.S. Tropical Cyclone 30 50+ 40 50+ Allison 2001
Tornadoes were a legitimate threat, too 96 hours continuous under a tornado watch - 4 full days 60 hours for Houston 157 tornado warnings Fri. morning - Mon. evening 24* confirmed tornadoes near Houston (*few surveys ) -23 of these Friday aftn-saturday night
Environment east/northeast of center Late afternoon/evening Aug. 25 SIGNIFICANT TORNADO PARAMETER RADAR COMPOSITE INFRARED SATELLITE
Environment east/northeast of center Late afternoon/evening Aug. 26 SIGNIFICANT TORNADO PARAMETER RADAR COMPOSITE INFRARED SATELLITE
Environment east/northeast of center Late afternoon/evening Aug. 27 SIGNIFICANT TORNADO PARAMETER RADAR COMPOSITE INFRARED SATELLITE
Harvey was a messaging nightmare! How do you process all this?! Record rainfall forecast Historic flooding Flooding- flash and then river Reservoirs and levee issues So many overlapping hazards!! 6 days of Tropical Storm and/or Storm Surge watches and warnings 4 consecutive days under a tornado watch A named storm helped!
Harvey: The Epitome of Overlapping Tornado and Flash Flood Warnings/Threats Tornado Warning calls to action and Civil Emergency messaging were sending conflicting messages: Seek shelter now Get on your roof
Life-saving Messaging Tweet Impressions: r 1,831,082 As water rises in the home, an electrocution threat can develop. Didn t want people to become trapped in their attics. Also can not see that they need to be rescued if in the attic.
Harvey Alert Fatigue and Mixed Messages Because of repeated tornado/flash flood warnings some likely turned off their phone emergency alerts. We want to make sure our most critical warnings/alerts are received, and people take appropriate actions. The Tornado Alert is Extreme and the Flash Flood Warning is Severe.
Tornadoes and Flash Flooding: Not a new problem Nielson et al., WAF 2015 400 overlapping warnings/year occurred on average between 2008-2014 68 verified TORFF events between 2008-2013...results indicate that TORFF events occur with appreciable frequency and in complex meteorological scenarios....present difficult challenges both from the perspective of forecasting and public communication. Life-saving actions for each hazard are contradictory! Fig. 1 from Nielsen et al, WAF 2015
Oklahoma City: May 31, 2013 Tornadoes and Flooding Recommendation: The NWS needs to develop warning protocol when there are multiple severe weather elements in the warning so that each element of the warning is weighted based on its urgency and severity. This protocol should include wording on how the public should prepare and respond to multiple, simultaneous dangers such as tornadoes and flooding.
Overarching Challenges NWS short fuse warning program is designed for individual threats Prioritizing and effectively messaging multiple and dynamic threats (can change during an event) Must not forget Human Element in catastrophic events Fear, anxiety, excitement, etc We tend to warn more, when perhaps we need to scale back to focus on the more serious threat(s)?
Harvey Example: Tornado > Flooding PRECAUTIONARY/PREPAREDNESS ACTIONS... Tornado Warning Heavy rainfall may hide this tornado. Do not wait to see or hear the tornado. TAKE COVER NOW! Tornadoes are extremely difficult to see and confirm at night. Do not wait to see or hear the tornado. TAKE COVER NOW! Friday Night (1249 AM 8/26/17) Landfall occurring
Harvey Example: Tornado > Flooding * At 1231 AM CDT, local law enforcement officials reported heavy rain across the warned area. Water is covering FM 655 and CR 521 near Rosharon. Flash Flood Warning Flash flooding is expected to begin shortly. Friday Night (1233 AM 8/26/17)
High-end EF1 Tornado Damage A tornado swept through Sienna Plantation in Missouri City, damaging at least 50 houses. Houston Press.
Example: FF Emergency > Tornadoes torrential rainfall rates of 4 to 6 inches per hour. Some of these areas have had already had 6 to 15 Flash Flood Emergency inches Flash flooding is ongoing and many rivers and bayous in the area are out of banks. This is a FLASH FLOOD EMERGENCY for portions of Galveston, Brazoria and Harris county. This is a PARTICULARLY DANGEROUS SITUATION. PRECAUTIONARY/PREPAREDNESS ACTIONS... Move to higher ground now. This is an extremely dangerous and life-threatening situation. Do not attempt to travel unless you are fleeing an area subject to flooding or under an evacuation order. Saturday Night (1130 PM 8/26/17)
Example: FF Emergency > Tornadoes IMPACT...Flying debris will be dangerous to those caught without shelter. Mobile homes will be damaged or destroyed. Damage to roofs, windows, and vehicles will occur. Tree damage is likely. Tornado Warning PRECAUTIONARY/PREPAREDNESS ACTIONS... TAKE COVER NOW! Move an interior room on the lowest floor of a sturdy building. Avoid windows. If you are outdoors, in a mobile home, or in a vehicle, move to the closest substantial shelter and protect yourself from flying debris. Saturday Night (1130 PM 8/26/17)
Historic flooding Dickinson, TX Aug 27th I-45 Sunday morning, Aug 27th A gasoline pump awning at the Dude Stop convenience store in Webster, Texas, is partially collapsed on Sunday, Aug. 27, after remnants of Hurricane Harvey inundated the area.(photo: Stuart Villanueva/The Galveston County Daily News via AP) Kelsey Walling/The Daily News Kelsey Walling/The Daily News Bay Area Houston Magazine
EF0 Tornado Damage at The Dude Stop A gasoline pump awning at the Dude Stop convenience store in Webster, Texas, is partially collapsed on Sunday, Aug. 27, after remnants of Hurricane Harvey inundated the area.(photo: Stuart Villanueva/The Galveston County Daily News via AP) Bay Area Houston Magazine
We Can Improve Need to be able to quickly adjust our calls to action and remove those that contradict a more severe hazard. I.E. in a tornado warning during a Flash Flood Emergency, actually state that the most dangerous threat is flooding. The other warning could be considered an awareness of a lesser threat, or not issued at all - if expecting a weak tornado or marginal flash flood threat. Concerning the Wireless Emergency Alerts (WEA) and the tornado warning call to action Take shelter now : we need to be able to change it when necessary. We could develop a trigger in the warning that would make this call to action selectable. For example: Avoid flood waters, take shelter if possible
A Suggested Call to Action TAKE COVER NOW! Move to an interior room on the lowest floor of a sturdy building. Avoid windows. If you are outdoors, in a mobile home, or in a vehicle, move to the closest substantial shelter and protect yourself from flying debris. Call to action changed to The main threat remains life threatening flooding. If your home is flooded, avoid flood waters. If possible, take shelter in an interior room. Avoid windows.
David J. Phillip / AP Thanks for your Attention!
Storm Prediction Center: www.spc.noaa.gov Contact: Roger.Edwards@noaa.gov (former NHC meteorologist) NWS Houston: www.weather.gov/hgx Contact: Jeffry.Evans@noaa.gov (former SPC meteorologist)