Sub-tropical / Surge Resources

Joe Sienkiewicz NOAA/NWS Ocean Prediction Center Ocean Prediction Center Subtropical : A non-frontal low-pressure system - characteristics of both tropical and extratropical . - non-frontal, originate over tropical or subtropical waters, - closed surface wind circulation about a well-defined center. - organized moderate to deep , lack a central dense overcast. - Partially baroclinic, ~ cold-core in the upper troposphere, - Radius of maximum winds relatively far from the center (> 60 n mi), and less symmetric wind field and distribution of convection than TCs.

- Can transition to a !

Ocean Prediction Center Ocean Prediction Center Ocean Prediction Center

Subtropical Cyclones

1996 – 2018 29 STs 9 seasons – 0 STs Max – 6 (2018)

NHC Products same as Tropical Storm! Sub-Tropical Cyclones - 2018

Alberto Beryl Ernesto

Leslie Debbie Oscar

Ocean Prediction Center Phases of Oscar

Low Sub-tropical Storm Tropical Storm

Hurricane Hurricane Hurricane Ocean Prediction Center Tropical Cyclone Frequency - Season

Ocean Prediction Center Tropical Cyclone Origins 0600 UTC 10 Jan

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Tropical Cyclone Origins

Ocean Prediction Center Summary Are subtropical cyclones becoming more frequent? Not enough evidence to suggest so! - We can diagnose structure much better than ever before. - Imagery - Remotely sensed data (passive and active) - Improved understanding of continuum of cyclone structure Hazards - Similar to a tropical storm but wind field may be larger and not as symmetric - Can transition into Tropical Storm or Hurricane

Ocean Prediction Center Resources

Ocean Prediction Center NOAA Tide Gauges

Ocean Prediction Center Boston Tide Gauge

15.16 feet MLLW Boston Harbor Tide Gauge Historic Crests Ocean Prediction Center Satellite Altimetry – Sea Level Rise Trends

Ocean Prediction Center Datum HAT - Highest Astronomical Tide - The elevation of the highest predicted astronomical tide expected to occur at a specific tide station over the National Tidal Datum Epoch (NTDE). MHHW - The average of the higher high water height of each tidal day observed over the NTDE. MLLW - The average of the lower low water height of each tidal day observed over the NTDE. NTDE - The specific 19-year period adopted by the National Ocean Service as the official time segment over which tide observations are taken and reduced to obtain mean values for tidal datums. It is necessary for standardization because of periodic and apparent secular trends in sea level. The present NTDE is 1983 through 2001 and is actively considered for revision every 20-25 years. Tidal datums in certain regions with anomolous sea level changes (Alaska, Gulf of Mexico) are calculated on a Modified 5-Year Epoch. https://slosh.nws.noaa.gov/ Definitions

SLOSH – Sea Lake Overland Surges from Hurricanes P-SURGE – Probabilisitc SLOSH ETSS – Extra Tropical Storm Surge Model P-ETSS – Probabilisitc ETS Surge Ensemble

Probabilistic Storm Surge

https://slosh.nws.noaa.gov/

Hurricanes – Probabilistic(P)-Surge

Summary • Familiarity with Water Level Products • Know your thresholds/ tolerance/ vulnerabilities • Action plan in place / exercise (storm events or astronomical high tides)