With all of the big words and hundreds of weather models being flung around social media in wake of the rapidly-strengthening Hurricane Harvey, the actual facts about and forecast information for the system can become confusing. Hopefully the information below will be both helpful and clear as to what to expect over the next week or so.
Yesterday evening, Harvey was nothing more than a weak tropical depression. For review, a tropical depression is a tropical cyclone in which the maximum sustained surface wind speed is 33 kt (38 mph) or less. It was a very unorganized, weak system at best, but, overnight, experienced rapid intensification. What does this mean? Overnight, Harvey increased exponentially in organization, size, and strength. As of early this morning, Harvey had strengthened into a tropical storm, a tropical cyclone in which the maximum sustained surface wind speed ranges from 34 kt (39 mph) to 63 kt (73 mph). A well-defined, closed center of circulation was also found, with sustained winds of 65mph and gusting higher. Harvey also developed a distinguished eye which is visible on current GOES-16 satellite imagery.
This afternoon, Harvey recon missions discovered that Harvey had strengthened into a hurricane, a tropical cyclone in which the maximum sustained surface wind is 64 kt (74 mph) or more, with 85 mph sustained winds, and gusts to 95 mph. The storm continues to strengthen and deepen as a low pressure system, and this likely won't end until landfall. Let's take a look at some of the specifics of Hurricane Harvey:
Harvey continues strengthening this afternoon, with a well-defined eye and sustained winds of 85 mph. Currently, the storm is positioned in the western Gulf of Mexico, moving NNW at 10 mph. The waters where Harvey is located are a very warm 87-91F, or 31C. Typically, sea surface temperatures only need to be 78F or 26C for tropical cyclone development and maintaining. This means that the waters under Harvey are MORE than supportive of strengthening over the next 24 hours.
Next, the wind shear aloft of Harvey is very weak, which is also good for sustaining and strengthening tropical cyclones. Currently, wind shear near the storm is favorable (green) and we expect conditions to remain this way through tomorrow.
Lastly, upper level divergence will also aid in strengthening of the system, as it allows for air to be displaced once it rises, which then allows for more lift to aid in the development of stronger convection.
All of the aforementioned items will aid in the overall strengthening of the storm. The latest model guidance is supportive of Harvey strengthening into a MAJOR hurricane, a hurricane that is classified as Category 3 or higher (96–112 knots, 111–129 mph). The latest NHC advisory suggests it may intensify to near Category *4* strength by landfall. Harvey will make landfall near Corpus Christi late tomorrow night/early Saturday morning. The storm will likely meander through the southeastern portion of the state for 5-7 days before finally moving north out of the area. A look at the official National Hurricane Center forecast for the next 5 days is shown below:
Beyond the next 5 days, some uncertainty remains for Harvey. The latest ensembles continue to support a track of a weaker low pressure system into the southern Ohio Valley by day 10 (next Saturday). This would bring higher dew points, cloud cover, and precipitation to the eastern Ag Belt, but confidence is only medium at this time.
As mentioned previously, SIGNIFICANT physical and economic impacts are expected in southeastern Texas. Harvey will likely make landfall as a MAJOR HURRICANE, with sustained winds of over 100 mph at the surface. The new HMON hurricane model (shown below) suggests winds of 135 mph at landfall.This level of winds can, and likely will, damage houses, trees, vehicles, and commercial buildings and is life-threatening if outdoors.
The latest wave models point to the possibility of 40+ FEET waves crashing into southeastern Texas tomorrow night and Saturday morning. These are very life-threatening waves, as they come on land and pull items back into the ocean. Storm surges are the number one killers in hurricanes. Below are forecast wave heights for Friday at 8pm EDT.
Next, flooding is of course a BIG concern with this system, not only because of the tropical rains, but because of the long duration that the system is likely to remain over southeastern Texas. Rainfall of over 20-30" will be possible, with locally higher amounts. The new GFS model shows this potential:
Lastly, one impact of tropical systems that many people are unaware of is tornadoes. In the outer rain bands of tropical systems, brief tornadoes are likely to spin up. While larger magnitude tornadoes aren't usually a threat at this time, damage to property and life is still possible and warnings should be heeded as normal.
Economically, Harvey will impact millions of people and many housing and commercial areas. Aside from that, flooding rains will damage farm fields and crops, as well as put a strain on the oil industry.
Many hurricane warnings have already been issued for the southeastern Texas coastline, as well as storm surge warnings, flash flood warnings, and tropical storm warnings as shown below:
Fun fact: it has been 4,322 days since the last major hurricane landfall in the United States- Hurricane Wilma on October 24, 2005.
If you are in any of the highlighted areas above, precautions should be taken IMMEDIATELY to prepare for the coming hurricane! We will have continued updates on social media throughout the system. Be sure to follow us on Twitter @tdswx @b_carp01, and @met_cooper for further information!