Hurricane Harvey: August 25, Update B

Wow, what a day!! Between 8-10pm CDT, Hurrricane Harvey made landfall between Port Aransas and Port O’Connor in Texas, officially as a category 4 storm. It looks like the Aransas Wildlife Refuge took the brunt of the initial landfalling eyewall winds. His official winds were at 130mph at landfall, making him barely a cat 4 storm (cat 4 range: 130-156mph), central pressure was 938 mb.

He is currently inland at 28.3N, 97.1W, heading NW at 6mph and is weakening. The pressure has increased to 950mb, and winds are now officially 115mph making him a weak cat 3 storm (cat 3 range: 111-129mph) - so still a major storm. 

He definitely intensified in the last few hours before landfall which we know from his very strong eye, which can still be seen in the visible satellite imagery, even though it is night now:

He also had a lot of convection, although less than I’ve seen in other storms. However, it is still in the red end of the spectrum, which translates to tornadoes and very strong thunderstorms:

Even after landfall, his structure continues to remain strong throughout the troposphere, with a strong signal for vorticity (circulation) in the upper levels of the troposphere (200mb):

This is also reflected again by the strong eye that we see, even though he is over land.

In looking at the winds and storm surge on the ground from Tides Online, Port Aransas had over 5 feet of storm surge and winds peaked there at around 55 knots, which is around 65mph:

After crossing the Aransas Wildlife Refuge, Harvey made a second landfall on the northeastern shore of Copano Bay, which also had a tide gauge sensor measuring sea level:

You can see that the water level signal here is interestingly different from Port Aransas. In this case, the water level dropped as the storm approached. Remember, a low-pressure system such as a tropical storm rotates counter-clockwise, so as it approaches land, places to the south of the eye will have water pushed offshore and will see a dip in sea level at the coast (depending on local geography), and that is what we see very beautifully here – it looks like his eye went just north of this station. The wind sensor maxed out at around 70 knots, which is over 80mph (cat 1) before it looked like it ‘broke’ (I assume). I think it is impressive that the sensor managed to record winds that strong.  We know the winds got stronger because if you look at the air pressure at the time the wind sensor got to 70 knots, it is still dropping which means that the eye was still approaching.

This storm really showcases that there is still something major that is missing in our understanding of intensity forecasting for storms, and our predictive capabilities for the intensity for storms is really very poor (three days ago the NHC and I were thinking he would be a strong TS/weak cat 1 at landfall!!). We don’t have sensors on the ground (or at sea) that are strong enough to really measure the data when a strong storm passes by, which means we only have estimates of how strong they get. We do have some amazing satellites though – and although they cannot give us accurate real-time wind speeds, we can see some amazingly fine-scale structure in the storm. This visible satellite image in particular is truly a hypnotic work of art! It is an experimental product from the Regional Mesoscale and Meteorology Branch at Colorado State University and shows the eye of Harvey in close up from the GOES-16 satellite:

I highly recommend you see the actual movie of these satellite images! It is really breathtaking. 

At the end of the day, there is very little difference between calling a storm a cat 3 at 129mph, and calling it a cat 4 at 130mph. That is a judgement call because the instruments are not accurate enough to really distinguish. But regardless, this was definitely a very strong storm! 

It is too soon to say what the extent of the damage is, especially as he is still a major hurricane, with category 3 winds... so we will wait until tomorrow. 

Until then!

J.

-->

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm
-------------------------------
DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.