The Importance Of Post-Season Hurricane Verification

GWCC_Feed | May 1, 2019 @ 2:30 pm

After conducting a post-storm analysis, @NHC_Atlantic determined that Hurricane #Michael‘s estimated intensity at landfall was 160 mph, making it only the fourth Cat. 5 hurricane on record to make landfall in the U.S. More: https://t.co/i18OBJ6PYC pic.twitter.com/Czaw1kPsNz

— NOAA Satellites (@NOAASatellites) April 19, 2019

DISCUSSION: Tropical cyclone (hereafter TC) intensity continues to be a fundamental forecasting challenge and despite the multitude of data outlets at the ready, real-time analysis does not always allow for precise estimates. However, a positive that arises with many datasets is the ability to further examine the true intensity and track of a previous season’s TCs. This analysis is known as a retrospective analysis (or reanalysis) and it is exactly what is done with each TC that formed in the previous season. Recently, Hurricane Matthew (Atlantic) was reclassified as a category 5 hurricane on the Saffir-Simpson scale at landfall which made it the fourth category 5 hurricane to impact United States soil in recorded history (the previous three were the Labor Day Hurricane of 1935, Camille in 1969, and Andrew in 1992). In real time, peak wind speeds in the eyewall of Matthew were estimated to be 155 mph but the post-season reanalysis revealed that peak wind speeds were in fact closer to 160 mph. A small change such as this may seem small on paper so it does beg the question, “what is the real importance of such a small upgrade?”

To understand the previous question, one must understand the procedure and subsequent impact of retrospective analyses. For brevity, the most significant points during the reanalysis run is explained. During a real-time observation and forecast, forecasters ingest large quantities of data from several ground-based and satellite-based products in order to generate a more profound analysis of the ongoing TC. These include observations from aircraft reconnaissance, surface station-reported winds, cloud-top based satellite intensity estimates and, if close enough to land, Doppler radar velocities, among many other viable datasets. These “raw” datasets are then quality-controlled to mask out any noise or contamination in the data fields and are then passed through post-processing routines to generate the accurate analysis fields. Ultimately, all of the available products are given consideration and are consulted simultaneously for any positive or negative discrepancies compared to the estimates during real-time. In the case of hurricane Michael, the peak wind speed of 160 mph was detected using a combination of the aforementioned datasets, and this peak occurred as the storm was nearing landfall near Mexico Beach, FL. As mentioned previously, some of the data used in a reanalysis may not have been made readily available during the real-time event which further enhances the significance of a reanalysis.

In short, real-time analyses of TCs can be a significant challenge for forecasters to make a precise estimate on TC track and intensity given the pressures of pushing out timely forecasts for the general public. However, going back to re-examine storms with the potential to access more data than what was made available during a real-time event allows for the forecasters to return and appropriately adjust the TC’s. As the availability and portability of weather data continues to expand, more tools and reference datasets would continue to aid forecasters in making more accurate predictions for TC track and intensity in years to come.

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