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12 exceptional facts from official Hurricane Harvey report

Jaclyn Whittal

Friday, January 26, 2018, 17:02 - Some five months after the fact, Hurricane Harvey is breaking more records now that the official summary from the National Hurricane Center has been released. Not only did the hurricane end the 12-year drought for major land-falling hurricanes, it is also now the second-most expensive hurricane on record, next to Katrina. We explore the storm's exceptional features, both in its meteorological sense and its historical sense.

1. Harvey has broken the record for the most rainfall in any tropical system. Large sections of southeastern Texas received 3 ft or more of rainfall in Harvey which totaled to over 60" based on the duration of the storm from August 17 to September 1. Harvey was the most significant tropical cyclone rainfall event in United States history, both in scope and peak rainfall amounts, since reliable rainfall records began around the 1880s. The highest storm total rainfall report from Harvey was 60.58 inches near Nederland, Texas.

While Harvey was very slow-moving over Texas, the heavy rainfall may have had more to do with an adjacent frontal zone. Slightly cooler and drier air over the southern United States behind a weak front situated across the Houston Metro area likely enhanced surface convergence and lift within the very warm and humid air on the eastern side of Harvey, leading to several episodes of heavy rain.  

2. Harvey was the first major hurricane (category 3 or stronger) to make landfall in the United States since Wilma in 2005, ending a record 12-year span which no hurricanes made landfall at such an intensity in the country. 

3. Harvey gained strength very rapidly in only two days. The storm, which had weakened after passing over the Yucatan Peninsula, regenerated as a poorly-organized tropical depression late on August 23, after which Harvey began to rapidly intensify in an environment of light shear, very warm water and high mid-level moisture. The storm turned northward, steered around the western edge of the distant subtropical ridge, and the track gradually bent toward the northwest. By August 24, a large mass of deep convection formed over the center, and an eye was noted that day. Harvey became a hurricane later on August 24, and by that night a well-defined eye appeared in infrared satellite pictures. The hurricane reached category 3 status by midday on 25 August 2017, and then strengthened further to a Category 4. 

Watch below: The scariest moments from The Weather Network's coverage of Hurricane Harvey

4. Harvey's eye did not make landfall anywhere near Houston Metro. Harvey made landfall at San José Island, Texas, at peak intensity, followed by another landfall at Holiday Beach at Category 3 intensity.  Although the center passed well south of the Houston Metro torrential, heavy rain fell in many locations near a stationary front on the north and east side of Harvey. The consistent rain was caused by feeder bands of moisture churning around the tropical system for days. 

5. After striking land, Harvey maintained hurricane strength for 2 days. Although it weakened as its speed slowed to a crawl, Harvey didn't weaken to tropical storm strength until August 26. This is very impressive as most hurricanes would normally interact with land and become much weaker much more quickly. 

6. The storm killed 68 people, with the majority being flood-related deaths. Over half of the deaths (36) were in Harris County in the Houston Metro area. Harvey is the deadliest U.S. hurricane in terms of direct deaths since Sandy and is the deadliest hurricane to hit Texas since 1919. About 35 additional deaths are ascribed to indirect causes, such as electrocution, motor-vehicle crashes and isolation from necessary medical services.

(Related: Staggering pictures of Harvey's rainfall and flooding)

7.Tornadoes are common with land-falling hurricanes, as there is enhanced amount of available wind shear, or winds changing direction with height. In total, there were 57 tornadoes reported within the storm's convective feeder bands off the Gulf of Mexico. Fortunately, almost all of the tornadoes were weak, of EF-0 and EF-1 intensity, with generally minor damage, few injuries and no deaths attributed to them.  

8. A hurricane's strength is measured by its central pressure, given in units of millibars - the lower the pressure, the stronger the storm. The minimum pressure of Harvey is estimated to have been 937 mb. The lowest observed pressure on land was 940.8 mb reported by a storm chaser in Rockport at on August 26. 

9. The highest observed sustained winds on land were 96 knots, or 110 mph, near Aransas Pass. The highest observed gust was 126 knots near Rockport, Texas, near where the storm made its official landfall as a Category 4 hurricane.

Must see: View of Harvey from space

10. The storm surge was not as high as many other hurricanes. The highest measured water level by a tide gauge was 6.7 ft above Mean Higher High Water (MHHW) at a Texas Coastal Ocean Observing Network (TCOON) site at Port Lavaca. Copano Bay, where Harvey made its second Texas landfall, also had significant storm surge flooding of 4 to 7 ft above ground level. Onshore winds to the east of Harvey’s Texas landfall locations likely produced storm surge inundations of 4 to 7 ft above ground level along the barrier island from Port Aransas to Matagorda, but hard to know for sure as there are no reporting stations in that area. 

11. By August 29, 2017 approximately 13,000 people had been rescued across the state while an estimated 30,000 were displaced due to the flooding from the storm. Additionally, throughout Texas more than 300,000 people were left without electricity and billions of dollars of property damage was sustained. 

12. The latest NOAA damage estimate from Harvey is $125 billion, with the 90% confidence interval ranging from $90 to $160 billion. The mid-point of the estimate would tie the damage cost of Katrina (2005) as the costliest United States tropical cyclone, which was also $125 billion. However, the unadjusted costliest tropical cyclone list is not the most relevant record to examine because of inflation and other cost increases since 2005, according to NOAA.

One of the big questions on everyone's minds after such a massive flooding event is: Can this happen again? Will the next storm bring even more rain?

We are learning that climate change is expected to lead to a greater incidence of high-intensity hurricanes, which, together with rising sea level, will produce increased risk of storm surge flooding, and it is very possible that more hurricanes could produce substantially more precipitation as the atmosphere and oceans warm. For all these reasons, it is important to continue to monitor each storm and study its attributes and its characteristics. We will do this as we look to this Hurricane season for 2018-2019. 

Source: NOAA National Hurricane Center

Watch below: We simulated a Category 2 hurricane; see Frisbee versus winds

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