The 12-year drought of major hurricane landfalls in the U.S. is over, with catastrophic impacts in Texas. Predictions of Hurricane Harvey illustrate the realization of extended- and long-range hurricane forecasts.
This blog post analyzes the forecasts of Hurricane Harvey made by my company Climate Forecast Applications Network (CFAN), and also by the National Hurricane Center.
The models included in this analysis are:
- ECMWF: 15-day HRES and ENS, and monthly (ENS extended)
- NOAA: 15-day GFS and GEFS
- NHC: HWRF, HMON
- CFAN: calibrated tracks and intensities for ECMWF and NOAA models
The images of tracks and intensities from the NOAA GEFS and ECMWF shown here are CFAN’s calibrated tracks and intensities. For further information about CFAN’s tropical cyclone forecast products and methods, see [link].
Hurricane Harvey – overview
An extensive summary Hurricane Harvey is provided by the Wikipedia:
Hurricane Harvey is a currently active tropical cyclone that recently made landfall in the US state of Texas as a Category 4 hurricane. It is the first major hurricane to make landfall in the United States since Wilma in 2005, ending a record 12-year period with no storms making landfall in the U.S. as a major hurricane.
Harvey developed from a tropical wave to the east of the Lesser Antilles on August 17. Upon entering the Caribbean Sea, Harvey began to weaken due to moderate wind shear and degenerated into a tropical wave early on August 19. [Harvey redeveloped] over the Bay of Campeche on August 23. Harvey then began to rapidly intensify on August 24, regaining tropical storm status and becoming a hurricane later that day. Harvey’s intensification phase stalled slightly overnight from August 24–25, however, Harvey soon resumed strengthening and became a Category 4 hurricane late on August 25. Hours later, Harvey made landfall near Rockport, Texas, at peak intensity.
The story of Hurricane Harvey is not yet over, as it continues to produce catastrophic rainfall in Texas and seems likely to re-enter the Gulf for some intensification and 2nd landfall in Texas or Louisiana.
Given the consistent track predictions among models and with time, after re-genesis on 8/23 attention turned to the intensity forecasts. On 8/24, Harvey began to rapidly intensify.
The intensity forecasts shown below include the GFS (dark blue), ECMWF HRES (red), ECMWF clustered ensemble members (black), HWRF (yellow-orange), and HMON (green).
HWRF was the first model to pick up hints of rapid intensification, on 8/24 00Z. The first model to predict Cat 3 was GFS at 8/24 12Z. HMON was the first model to approach a Cat 4 forecast 8/25 00Z.
Closer to landfall, ECMWF DET (HRES) predicted the highest intensity (approaching Cat 4). Note, after landfall, the NOAA/NHC models predict a rapid fall off in intensity, whereas ECMWF predicts re-intensification about 4 days after initial landfall. This third act for Harvey is still playing.
Summary of forecast model performance
Since Hurricane Sandy in 2012 and the exceptionally accurate forecast of ECMWF as much as 6 days in advance, there has been a battle of the hurricane forecast models: NOAA/NHC versus ECMWF. For Harvey, all of the forecast models both performed very well, albeit with some differences.
Summary of the forecasts, using CFAN’s calibrated ECMWF and NOAA GEFS forecasts:
- Harvey’s first genesis predicted by ECMWF & NOAA on 8/14, three days in advance and 12 days before landfall
- Significant probability for tracks in the GoM predicted on 8/18 by ECMWF (56%) & NOAA (41%)
- (Re)genesis: ECMWF had earlier, more consistent prediction
- >50% probability of TX landfall: ECMWF (8/22 0Z); NOAA (8/21 0Z). Edge to NOAA.
- Track forecast solidifies: NOAA 8/21 12Z; ECMWF 8/23 00Z
- Best 4-day track forecast: NOAA GFS
- Earliest prediction of Cat 3: NOAA GFS 8/24 12Z
- Earliest prediction of (near) Cat 4: HMON 8/25 00Z
Harvey in context
I’m sure you won’t be surprised to hear people blaming Harvey on global warming. How unusual was Harvey? Well, it will definitely be in the record books for ending the 12-year drought of major hurricanes striking the U.S.
Phil Klotzbach has prepared this list off Cat 4-5 U.S. landfalling hurricanes:
This list reminds us how awful things were. Apart from the horrendous 2004/2005 years, we have been pretty lucky in recent decades.
Anyone blaming Harvey on global warming doesn’t have a leg to stand on.
Harvey will be in the record books for almost unbelievable amounts of rainfall (the final tally is not in yet; unfortunately it will still be raining in TX for several more days, with the potential doubling of the amount that has already fallen). While there was a large amount of water vapor ingested into Harvey, the huge amounts of rain are associated with Harvey’s stalled movement, while still close enough to the Gulf to continue to suck in moisture.
Read more at Climate Etc.