Hurricane Milton (2024): Location of Peak Winds ...

Jeff WatersOctober 24, 2024

There has been a lot of discussion regarding the exact location of the peak surface winds at the time of Hurricane Milton's landfall just after 0000 UTC on Thursday, October 10.

Looking at the Moody's RMS HWind snapshot released at this time (see figure 1 below), peak surface winds consisted of a surface wind speed maximum of 93 knots (107 miles per hour) southeast of the tropical cyclone, just south of Sarasota, FL on the right-hand side of the storm, and a secondary maximum occurred just west of Tampa Bay, north of Milton's eyewall.

The secondary maximum was due to the storm interacting with a mid-latitude jet over the Gulf of Mexico leading up to landfall, resulting in a swath of strong winds wrapping around the back of the system (i.e. to the north).

Figure 1: Within the Exposure IQ application on the Moody's Intelligent Risk Platform, the HWind snapshot showing peak 3-sec gusts (mph) for HU Milton as of October 10, 2024 at 0000 UTC. Winds are marine over open water and open-terrain over land.

Examining other wind field solutions, one has indicated that the peak surface wind observation occurred approximately 19 miles (30 kilometers) west of the storm center during landfall, with magnitudes near 100 knots (115 miles per hour).

We hypothesize that this is largely informed by a single Stepped Frequency Microwave Radiometer (SFMR) platform onboard the Air Force Reserve (AFR) flight that surveyed Milton prior to landfall.

There are two problems with these observations:

• They were associated with high rainfall rates (25 millimeters per hour); heavy rain contaminates SFMR and yields a high bias.
• SFMR has been consistently unreliable in 2024 such that NOAA flights have stopped transmitting its data.

Moody's RMS HWind snapshots, including those for Hurricane Milton, are informed by observational data across over 30 sources.

For Milton in particular they were constructed with wind observations from a combination of flight-level data (AFR, NOAA42) reduced to the surface, dropsondes, moored buoy data, and surface stations (e.g., Automated Surface Observing System (ASOS), Coastal Marine Automated Network (C-MAN), Florida Coastal Monitoring Program (FCMP), Citizens Weather Observer Program (CWOP), among others.

The screenshot below from the HWind QC App - used to ingest, QA, and standardized observational data during real-time events, reflects the observational data used to inform the previous snapshot from October 10, 2024 at 0000 UTC.

Of a total of more than 3,800 individual data points used, figure 2 shows wind vectors from all observations adjusted to surface winds across all sources, where figure 3 shows raw flight-level AFRC (red) and SFMR (orange) platforms greater than 100 knots (115 miles per hour).

Note the flight-level winds greater than 100 knots are to the east / southeast of the storm's center (represented by a blue circle). SFMR observations (orange) show over 100 knots winds to the left hand side of the storm. They are shown for comparison only, and were not used to inform the snapshot.

Figure 2: Screenshot of the HWind QC App and the observational data used to create the Hurricane Milton snapshot on October 10 at 0000 UTC. The data shown here - filtered to only represent winds of 100 kts and above - is from the last AFR (bright red) and NOAA (dark red) flights before Milton's landfall (taking place between 1800 10-09 and 0030 UTC 10-10). Winds are shown as raw flight-level (not surface corrected).

The orange is the SFMR (valid at the surface) from the AFRC flight. Note the SFMR data is shown here for comparison only. It was not used in the snapshot. You can see that all flight-level winds greater than 100 kts are to the E/SE of the center at 0000 UTC (center represented by blue circle). There were several 100+kt SFMR observations on the LHS of the storm (with respect to the storm heading).Figure 3: The data shown here is from the last AFRC (bright red) and NOAA (dark red) flights before Milton's landfall (taking place between 1800 10-09 and 0030 UTC 10-10). Winds are shown as raw flight-level (not surface corrected). The orange is the SFMR (valid at the surface) from the AFRC flight.

The SFMR is shown here for comparison, we did NOT use it in the snapshot. In the image the 100-kt threshold is on, masking anything below 100 kts. You can see that all flight-level winds greater than 100 kts are to the E/SE of the center at 0000 UTC (center represented by blue circle). There were several 100+kt SFMR observations on the LHS of the storm (with respect to the storm heading).

What About the Rest of the Hurricane Milton Footprint?

Ultimately, Hurricane Milton resulted in dual swaths of strongest winds at and shortly after landfall: one to the south of the storm associated with the tropical portion of Milton, and one that wrapped around the back of the system (i.e. to the north) associated with its interaction with the extra-tropical system.

That bifurcation in the wind speed maxima can be seen in the final HWind Cumulative Wind Hazard footprint in the image below. Also visible in this image is the observed expansion of Milton's wind field prior to landfall.

While the storm's Vmax weakened leading up to landfall, the interaction with the jet stream induced asymmetries that broadened its wind footprint.

Figure 4: Within the ExposureIQ application on the Moody's RMS Intelligent Risk Platform, the final HWind Cumulative Wind Footprint showing peak 3-second wind gusts from Hurricane Milton (2024) as of October 10, 2024 at 1200 UTC. Winds are marine over open water and open-terrain over land. Note the swaths of strongest winds to the north and south of where the storm tracked.

Overall, rigorous quality control of the breadth of observational data in real-time ensures the data informing the snapshots and cumulative footprints is credible, thus providing confidence in the magnitude and spatial distribution of the surface wind fields that are reflected in those products. As such, Moody's is confident in our current state of the snapshots and cumulative footprints for Hurricane Milton, which do not include SFMR.

We'd like to thank the following people on the HWind team for their contributions to the above, including Jeremiah Otero and Randall Gaynor.

Jeff Waters

Director, Model Product Management, Moody's

Jeff Waters joined Moody's RMS in 2011 and is based in Bethlehem, PA. As part of the Product Management team, he is responsible for product management of the Moody's RMS North Atlantic Hurricane Models.

Jeff provides technical expertise and support regarding catastrophe model solutions and their applications throughout the (re)insurance industry. He also generates product requirements for future updates and releases, and helps develop the overall product strategy, messaging, thought leadership, and collateral to ensure its commercial and technical success.

Waters' background is meteorology and atmospheric science with a focus in tropical meteorology and climatology. Jeff holds a B.S. in Geography/Meteorology from Ohio University ('09), and a M.S. in Meteorology from Penn State University ('11). He is a member of the American Meteorological Society, the International Society of Catastrophe Managers, and the U.S. Reinsurance Under 40s Group, Inc

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