Hurricane Season Preparedness 2019 National Weather Service New Orleans/Baton Rouge Weather Forecast Office

2018 Seasonal Recap 15 Tropical Storms 6 Hurricanes 2 Major Hurricanes Notable Storms: BOTH major hurricanes affected the US Florence – winds weakened before landfall, but still produced catastrophic flooding Michael – landfall as a category 4 resulting in widespread wind and storm surge damage 2005 is still the most active with 28 named storms, and 7 of them major hurricanes

Colorado State U. Forecast Caution: it only takes one 2019 Seasonal Outlook Average Colorado State U. Forecast NOAA forecast (Release May 23) Named Storms 12 13 ?? Hurricanes 6 5 Major Hurricanes 2 Caution: it only takes one

2019 Seasonal Forecast Seasonal forecasts do NOT tell you: Where storms will make landfall How strong they will be at landfall Seasonal forecasts only give a general idea of the potential for overall basin activity Reality: We have to plan as though we will be impacted EVERY year

Lead Time is Great, but… Five-day plans are great, but you won’t always have five days of lead time on the Gulf Coast

Lead Time is Great, but… Five-day plans are great, but you won’t always have five days of lead time on the Gulf Coast Hurricane Michael 2018 Wasn’t classified as a tropical storm until about 72 hrs before landfall as a category 5 hurricane Intensified from 75 mph winds (category 1) to 130 mph winds (category 4) in 42 hours

Lead Time is Great, but… Five-day plans are great, but you won’t always have five days of lead time on the Gulf Coast Hurricane Camille 1969 Wasn’t classified as a tropical storm until about 80 hrs before landfall as a category 5 hurricane Intensified from 75 mph winds (category 1) to 120 mph winds (category 3) in 24 hours

Lead Time is Great, but… Five-day plans are great, but you won’t always have five days of lead time on the Gulf Coast Hurricane Cindy 2005 Wasn’t classified as a tropical storm until about 48 hrs before landfall

Lead Time is Great, but… Bottom Line: You won’t always have a 5 day lead time on Gulf of Mexico storms, so timetables need to be adaptable! For thought… Could you execute your plan in only 3 days? How about as few as 2?

Hurricane Forecast Verification Track forecast skill has improved tremendously A 3-day forecast today is about as accurate as a 1-day forecast was in the 1990s Since 2005 (Katrina), the 3-day forecast error has been cut in half (from ~190 miles in 2005 to ~90 miles in 2017)

Hurricane Forecast Verification Intensity forecasts have only shown modest improvement In 2017, the 48-hr intensity error was about 13mph, or approximately 1 Saffir-Simpson category This is why planning for one category higher than forecast is still a good course of action

Rapid Intensification One reason intensity forecasts aren’t improving as fast as track forecasts – rapid intensification An increase of 30 kts (35 mph) in 24 hrs Notable Examples: Hurricane Michael 2018  90mph to 140mph in 24 hours (still rapidly intensifying up to landfall) Hurricane Gustav  75mph to 145mph in 24 hrs (before landfall in Cuba) Hurricane Katrina 2005  115mph to 170mph in 18 hrs Hurricane Camille 1969  105mph to 175mph in 24 hrs

Atlantic Tropical Cyclone Deaths by Hazard Flooding from storm surge and fresh water (rain) accounts for over three quarters of deaths directly attributable to Atlantic Basin Tropical Cyclones

The Storm Surge Threat

Factors Influencing Storm Surge Where the circulation center crosses the coast Direction of storm motion relative to the coast Wind strength (storm intensity) Radius of maximum winds (eye size) Overall size of storm (outer wind radii) Slope of the continental shelf Shape of the coastline and other coastal features (barrier islands, bays, rivers, levees, etc) …It’s Complicated!

Landfall Location - Comparison Landfall to the west Landfall in the middle Landfall to the east Bottom Line: Small changes in the storm can lead to big changes in the surge.

The Inland Flooding Threat

Factors Influencing Heavy Rainfall and Inland Flooding Forward Speed (slower means more rain) Size (bigger means more rain) Rain Rate (atmospheric moisture content) Vertical Wind Shear (more rain on one side) Interaction With Fronts/Upper-Level Troughs …It’s Complicated!

2017 Hurricane Harvey Highest 6-day storm totals: Nederland, TX: 60.58” – new US record! Groves, TX: 60.54”

2017 Tropical Storm Cindy Heavy rain often falls in “bands” and can mean sharp gradients in recorded rainfall It’s difficult to predict where these bands will set up more than a few hours in advance Heavy rain often falls in “bands” and can mean sharp gradients in recorded rainfall.

Un-named Low: Rainfall Impacts

Rainfall Risk Considerations Recurrence intervals like “100-year” or “1000-year” storm can be misleading Those terms are really a representation of annual risk 100-year storm  1% annual flood risk 500-year storm  0.2% annual risk 1000-year storm  0.1% annual risk Risk remains the same every year, even if a similar event happened recently!

Rainfall Risk Considerations Flood risk is cumulative!

Product Review For the 2019 Hurricane Season

Time of Arrival Graphics NHC Arrival Timing Graphics Preparations become dangerous once winds reach TS force Graphics account for forecast uncertainty (track/intensity/size) “Earliest Reasonable” graphic - best for users with low tolerance for risk “Most Likely” graphic - best for explaining when all preparations should be completed prior to onset of dangerous conditions

Heavy Rainfall Threat High Risk Days – Be Especially Vigilant Even Moderate Risk days carry an increased risk of life threatening heavy rainfall - flooding.

Potential Storm Surge Flooding Map (Inundation) This is ONLY surge flooding NOT the forecast - “Reasonable” worst case Only a 10% chance these values will be exceeded Subtle changes possible with each update No values shows inside risk reduction system

Storm Surge Watch/Warning Storm Surge Watch – there is a possibility of life-threatening storm surge inundation within 48 hours Storm Surge Warning –there is a danger of life-threatening storm surge inundation within 36 hours

Storm Surge Watch/Warning Will be tone alerted via NOAA Weather Radio Will likely be tone alerted via Wireless Emergency Alerts in 2019 CAN be issued for areas inside the risk reduction system

Storm Surge “Gotchas” Products only account for storm surge flooding They do NOT include fresh water (rain) flooding They do NOT include any drainage flooding (water flowing downstream) Tone alerts through weather radio and WEA will likely “over warn” some areas Weather radio alerts are parish/county based WEA are sent by cell towers covering the warned area and can still result in “bleed over”

Some Final Thoughts… Every storm is different! Pay attention to local NWS products (both official text products and graphics posted on social media and our website) and the local media to determine what the greatest impacts will be for the local area from a given storm. Be careful where you get your information. “Social mediarologists” sometimes post model forecasts with little context or explanation to get more “likes”. Single track model forecasts are almost never right, especially at long lead times. Make sure you’re getting information from a reliable and reasonable source.

National Weather Service New Orleans/Baton Rouge www.weather.gov/neworleans Facebook: NWSNewOrleans Twitter: @NWSNewOrleans 985-649-0429 504-522-7330 We answer the phones 24/7/365! Note: A recording will pick up and has some options for general information. If you have questions, there is an option to speak to a forecaster.