Storm prediction using CNAPS – a fully coupled atmosphere-ocean-wave modeling system

Hurricane Matthew is on track to become the first major hurricane to make landfall on U.S. shores since Wilma in 2005. National Hurricane Center (NHC) predicted Matthew could make landfall in Florida early Friday as a Category 4 hurricane. At the same time, Nicole to its east was just upgraded to Category 1 hurricane (Figure 1).


Figure 1. Visible image on Oct. 6 at 1:00 p.m. EDT from NOAA’s GOES-East satellite shows Hurricane Matthew as it regained Category 4 hurricane status. Hurricane Nicole is visible to the right. Image credit: NASA/NOAA GOES Project.

This is a rare phenomenon and how exactly the two tropical cyclones will interact with one another is too early to tell. NHC predictions suggest Nicole will likely nudge Matthew back to Florida and Bahamas again in a loop-de-loop early next week (Figure 2). The underlying three-dimensional ocean conditions will play a key role throughout this process. Accurately resolving the dynamic ocean temperature field and the momentum, heat and moisture flux exchanges across the air-sea-wave interface is in particular crucial for hurricane intensity forecast.


Figure 2: NHC prediction of hurricane Matthew’s track and intensity as of Thursday, Oct 6, 8 pm EDT.

At North Carolina State University, Ocean Observing and Modeling Group (OOMG) is using their Coupled Northwest Atlantic Prediction System (CNAPS) to closely monitor and predict Hurricanes Matthew and Nicole. CNAPS is a fully coupled Atmosphere-Ocean-Wave Modeling System, providing a unique capability to account for complex but important air-sea-wave interaction dynamics during storms and generate forecasts of simultaneous atmosphere, ocean and wave conditions.

CNAPS is operated on NC State’s high-performance supercomputer, providing daily nowcast and 3-day forecast for the entire Northwest Atlantic ocean. Routine model output include sea level air pressure, 10-m wind, significant wave height and directions, 3-dimensional ocean circulation, temperature and salinity (Figure 3).


Figure 3. Snapshots of CNAPS predicted concurrent marine weather, ocean, and wave conditions at 21:00 EDT, October 6. 2016, showing Matthew is accompanied with strong wind, current, and wave; so is Nicole, albeit with smaller size and scale. 

Near-real time model validations against HF radar surface currents and buoy measurements have been implemented and continue to be refined in CNAPS (Figure 4).  


Figure 4. Comparison between HF radar observed and CNAPS predicted surface current fields off Miami at 2100 EDT, October 5, 2016. CNAPS prediction shows that Matthew had a strong interaction with the northward flowing Gulf Stream and an energetic  cyclonic surface current gyre was generated. (HF data courtesy: Nick Shay, University of Miami)

Other interactive functions built into CNPAS include: isosurface maps of ocean current, temperature, salinity; visualizations of user defined station profiles and hydrographic transects, as well as 72-hour surface trajectory simulations of user defined “virtual particles” (Figure 5).


Figure 5. Virtual particle trajectories simulated by CNAPS.

To check out CNAPS predictions of Matthew and Nicole, and their concurrent ocean circulation and wave conditions, use this link.

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