What a Week

What a week meteorologically that shows the opposite ends of how great and devastating nature can be.  The week started with a rare eclipse that crossed the U.S. and ended with a tropical system that went from a depression to a Category 4 in 48 hours.

With daylight we are starting to see the initial impacts from a major hurricane landfall that made landfall at 10 pm CDT last night .  Given that this is the first major hurricane in the information mobile age there is just a wealth of information to take in that is almost overwhelming.  In fact, since this is the first major category 4 to make landfall since Hurricane Charley in 2004 it will likely provide very valuable data to the insurance industry, which has a lack of datasets for such events.  From mobile weather stations and surge devices being deployed ahead of landfall to mobile radar and drone aircraft, this will no doubt be one of the best documented major hurricane landfalls that has ever occurred.

However, I can’t stress enough that the event is not over. It is just starting, and as forecasted, the storm has slowed and is still expected to stall out over the next week and is expected to dump feet of rain along the Texas Coastline.

Harvey Landfall Details

Hurricane Harvey is now only the sixth Category 4+ landfall in Texas weather history (since 1851), and the 2nd in the last 100 years.  Below are the top ten strongest hurricanes at landfall and Harvey is the strongest since Charley in 2004, but likely won’t make it into the top ten in terms of wind and will be 14th in terms of pressure.

List of the strongest hurricane by wind speed to make landfall in U.S. Harvey will not make this top ten list.

In fact, what is more remarkable is from 1926-1969 (44 years) 14 Category 4 U.S. landfalls occurred, but since 1970-2017 (46+ years) only 4 Cat 4+ landfalls have occurred.  This is a decrease greater than 70%.  Statistically the 12 years without a major hurricane landfall will be very hard to replicate, but let’s hope this does not start a trend in the opposite direction.

As pointed out the building standards in Texas are not as good as other states, but the fact is even the best built homes are not designed to withstand category 4 winds. The heaviest wind damage from Harvey appears to be in Rockport, Fulton  area.  Thankfully Harvey’s highest winds likely occurred over Matagorda Island State Park and Aransas National Wildlife Refuge, where there are very few structures or population. This will no doubt limit wind damage form Harvey.

Area of landfall that shows overall luck played a roll in limited damage as a state park likely took on the strongest winds. Any other island like this along the U.S. coastline would be full of homes.

 

If Harvey would have tracked just 20 miles further south it would be a completely different story in Corpus Christi, which has sustained damage to buildings, but not like the Rockport area.

It would be rare for a surface observation to verify Harvey category 4 winds, but category 3 winds have been verified.  In fact, at 8:48pm CDT, the C-MAN station at Port Aransas, TX sustained 10 meters winds of 114mph with gusts to 131mph. Some other notable wind speed gusts were 110 mph at Copano Bay, 108 mph in Rockport and 102 mph in Aransas Wildlife Refuge, but as mobile station data is collected and communication is restored, more data will be collected providing even more high wind readings.  Another interesting observation is that the pressure gradient was very steep, with an air pressure of 994mb in Sinton, TX and 943mb or so in Rockport, TX  which is a difference of 51mb over 30 miles. This is why the winds were so strong but also indicates that the radius of maximum winds was quite narrow which will also limit damage over a large area.  However, it is known there are many high value homes in the area as lots of folks from Austin and San Antonio like going to the beach on weekends.

 

BMS iVision Max Wind Gust over the last 24 hours.

BMS iVision Max 1 Min Sustained Wind Speed showing the swath of Harvey and track. Notice the limited inland impacts from high winds.

The exact central pressure has yet to be verified as there are several storm chasers that recorded a pressure of 938 mb.  One notable chaser “icyclone” who likely holds the world record for a human to experience so many hurricanes worldwide said on twitter that this was “one of the worst I’ve been in”.  His calibrated pressure reading was 940.8 mb at 10:31 pm.  This could be very important as once again these readings could influence payout in the Cat Bond market, in particular the newly revised  IBRD / FONDEN 2017  Mexico’s Fund for Natural Disasters Bond that was revised to cover points in North Texas this go around, however, at this early stage it is unclear if the center crossed the box needed with a pressure of 930 mb.

Insured Loss

As mentioned above there are several cat bonds at risk of payout.  However, it is still too early to determine what the exact insured loss will be as the event is still unfolding with days of heavy rain yet to occur.  And with heavy rain still to fall in Harris County this will likely determine the overall event impact with a high percentages of flood-prone properties there.  It has been suggested that the LiveCat market was predicting a payout attachement point of $10B U.S. dollars, however Harvey strengthened right up until landfall and will stall out making modeling of this event very difficult.  The modeling that was provided yesterday will likely better account for the strengthening at landfall and new loss estimate will likely be revised upwards because of this.

Storm Surge

At this point in time the storm surge has not been as high as predicted as Harvey just did not have the overall size to cause devastating surge similar to Hurricane Ike, this will also limit some insured losses.

http://surge.srcc.lsu.edu/harvey_2017.html

https://tidesandcurrents.noaa.gov/quicklook/view.html?name=HARVEY

Various Storm Surge Readings from the landfall area.

Flooding Rains

As mentioned all week, flooding rain will be a major problem with Harvey stalling out.   The latest storm summary from the national weather service suggests rainfall totals are already approaching 15″ with several other spots closing in on 10″.

 

This is the latest 7 day forecast rainfall total.

Forecast

There is no change in Harvey’s forecast.   Harvey will slowly spin in the same spot for the next several days.   The option of a second landfall later next week are slowly dwindling off the table, but it can’t be ruled out at this moment as pointed out by the ECMWF model below