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Hurricane Harvey

star gazer

Hurricane Harvey looks set to be the first Major Hurricane to make landfall in the United States in over a decade and one of the most worrying aspects of it is the forecast for Harvey not to move very far for days after making that landfall, meaning a lot of rain will fall over a large section of the Texas coastal area for an extended period. 400mm to 650mm of rain could fall in a large area of the Texas coast and up to 900mm in isolated parts with storm surges of 1 to 3.5 meters. At the moment Minimum Central Pressure is 967mb with max sustained winds of 165km/h 105mph making it a Category two Hurricane. It is due to strengthen to a Category 3 Major Hurricane today and make landfall some time late Friday local time. Houston is forecast to get huge rainfall with actual landfall likely to be made somewhere near Corpus Christi.
NHC advisory 20 Wunderground

A report from the weather channel warning that it's the water (storm surge and rainfall flooding) that causes the most fatalities in these natural disasters:
https://twitter.com/weatherchannel/status/900838671775133696
The first rain bands are affecting land already. Donegal saw what can happen with a large amount of rain in a short space of time, Such a large amount of rain over an extended period will be an enormous test of communities and of their emergency response services.

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Wanderer78

friend lives in houston, current state of her local highway:

Somedude9

Wanderer78 wrote: »

friend lives in houston, current state of her local highway:

Holy fook! :eek:

Itssoeasy

I mean Corpus Christi and Galveston, and rockport Texas getting walloped but the Houston pictures and video I've seen is frightening. And an I right in thinking it'll move back out to see and come back in ?

Wanderer78

Somedude9 wrote:

Holy fook!

Basically same response I gave to her. Have a couple of more pics, will post tomorrow. Very scary though

pad199207

Signs that Harvey is slowly re strengthening again as it has moved over the gulf.

More robust convection redeveloping

MJohnston

Wanderer78 wrote: »

friend lives in houston, current state of her local highway:

Can't remember exactly where I read it now, but I do recall reading that Houston's freeways are designed to be part of flood relief strategies, in that they have been built to act as water channels during floods.

Wanderer78

MJohnston wrote:

Can't remember exactly where I read it now, but I do recall reading that Houston's freeways are designed to be part of flood relief strategies, in that they have been built to act as water channels during floods.

Seems a bit of an odd strategy, she said they are more or less stuck at home due to it, little bit of flooding on their own land to

sword1

I wouldn't like to be driving on those roads when the water recedes. You could be driving in a foot of water but the road could have collapsed and you would not be able to see it.

MJohnston

Well, I suppose you can pin that to the whole "Once in 500 years" problem, but it's certainly why people have been told not to evacuate, because the freeways are essentially designed to become rivers.

Meteorite58

Incredible rainfall totals so far

https://twitter.com/50ShadesofVan/status/902229957400780800

https://twitter.com/NWSHouston/status/902223339611189248

Charles Babbage

MJohnston wrote: »

Well, I suppose you can pin that to the whole "Once in 500 years" problem, but it's certainly why people have been told not to evacuate, because the freeways are essentially designed to become rivers.

Telling everyone to evacuate would indeed have caused a lot of problems and presumably there are many areas well above water. However, floods can be modelled in advance and many people should have been told to evacuate, depending on the detail of local topography. People in areas that would be inevitably flooded should have been driven out last Friday, not now requiring volunteers with boats to come and rescue them.

Cantona's Collars

Watching CNN last night and they had been in contact with the owners of an Alligator Park attraction near Houston. All the poisonous snakes etc. had been removed a few days ago but the problem now is that their fences which were erected higher than normal for a flood event are almost under water.Some 360 alligators can simply swim over the top of them and go where they like.

star gazer

Part of the reason Harvey was able to maintain itself with the dry air coming in at some levels, was it had flooded so much of the area it was on land over that it was in part like being over open water and recycled. Now over water moving at 6km/h East, 997mb and due to stay over water for another day or so. Forecast for Houston is hopeful that after today the worst of the rainfall should have passed it by, however there is a lot of pressure on the resevoirs, particularly Addicks dam where they may have to take some serious decisions with big implications. The path of this storm meant it has just kept putting some of its heaviest rain into the Houston area for days, some parts of which have now passed a full meter of total rainfall accumulation so far. Parts of Louisiana and possibly New Orleans itself are looking like getting very heavy rain which is seriously noteworthy, overshaddowed by what's happening around Houston.

Cantona's Collars

The 2 reservoirs they were worried about have started overflowing.

bnt

The worst rainfall appears to be over for Houston, according to the Chronicle. Most of the metro area can expect an average of 1.5 inches over the next two days, which is more "normal", but the flooding isn't over yet.

Measured rainfall figures for the last week, in inches (40 in = 1000mm):

:eek:

star gazer

Check out the far right of the bnt's above graphic 49.32 inches (1250mm) is a record for all the lower 48 States, pushing close to a Hawaii record of 52 inches. Harvey is over some churned up cooler water, further East there's above average warmth and some heavy rains are forecast for coastal Mississippi and Alabama as well as Louisiana. A serious worry is that when food waters recede that there will be a tragic cost in human lives. Harvey is moving at 7km/h NNE pressure 997mb.

bnt

Slightly adjusted figure being reported by the National Weather Service:

https://twitter.com/NWSHouston/status/902552433645277184

Note that these are only the gauges for Harris County, and it's been seen because this data is online. I wouldn't rule out the possibility of a higher figure coming to light from another county.

star gazer

Moving NNE at 11km/h which is helping to move the rainfall out of the Houston area even if a lot of rain has fallen quite close by. Minimum central pressure at 990mb (5mb drop in 3 hours) and it had made it up to 80km/h max sustained winds last night but down to 75km/h now. It's made landfall now. There's a curfew in place in Houston to prevent looting and even armed robbery. Harvey will travel inland on some flooded areas but it is not expected to hang around like it has done, while still raining heavily on areas as it passes through. The drier air getting into the circulation likely helped contain intensification.

Rainfall and wind totals so far 51.88 inches, over 1300mm in one reading at Cedar Bayou.

star gazer

The death total for Harvey is at 20 with the worry that it will take some time to fully assess the tragic loss of life and damage in general. There are still ongoing flood water dangers in the Houston area but just as the very heavy rain seemed to be sustained/stalled over the Houston area for much of the last few days, the centre of persistent phenomenal rainfall shifted North East to the area around Beaumont and a previous evacuee shelter in Port Arthur was flooded and people evacuated again. The rain is still ongoing in the Beaumont area. Rain totals going up for Louisiana particularly, Coastal Mississippi, Alabama and a small part of Florida. Massive flooding disaster from Harvey in South East Texas, that will take weeks, months and years to recover from. Roads became rivers.

Advisory 41A pressure 995mb, max sustained wind 65km/h, moving NNE at 13km/h inland Western Louisiana.

pauldry

Looked at ogimet and 553mm in Port Arthur in past 24hours

Thats about double the intensity of the heaviest rain in Malin Head last week but for a full day!

MJohnston

star gazer wrote: »

The death total for Harvey is at 20 with the worry that it will take some time to fully assess the tragic loss of life and damage in general.

Yeah, as I read about Katrina today, they have admitted they'll never know the precise figure for deaths, might end up being the same here.

Jpmarn

It is hard to imagine that more rain fell in parts of the Houston area in less than a week than we expect in a whole year in around Limerick, Ireland. 1000mm would count as a wet year in Shannon Airport.

Meteorite58

Interesting effects from Harvey as the flood waters flow back out to sea. I wonder will pollution be a factor.

https://twitter.com/NASAHurricane/status/903598922039529473

https://twitter.com/NASAHurricane/status/903597770778578945

Meteorite58

https://twitter.com/NOAASatellites/status/903356742104489986

MJohnston

A summary of how the different models performed for Harvey: https://arstechnica.com/science/2017/09/at-times-during-harvey-the-european-model-outperformed-humans/

Spoiler alert: ECM won.

star gazer

The rapid intensification of Harvey to a Cat 4 Hurricane over the Gulf of Mexico is noteworthy and could form part of the study into whether there is a direct link between a warmed world and more and more intense tropical storm activity in the Atlantic, and also in the Pacific. The way that it meandered and kept it's heaviest rainfall pushing onto the Houston area was stunning and though it is hard to say it because of all the lost lives and devastation, it could have been worse if it had not moved on just a few dozen miles to put another deluge onto the Beaumont area before finally moving out of the State. One of the reasons put out for not evacuating more people on foot of the forecasts was the harm that can be done in getting millions of people to evacuate at short notice. It looks prudent now to investigate how to more safely evacuate large numbers of people at short notice when the next major threat is forecast and not just in Texas. Tiered evacuations, readied evacuation centres and good coordination between all authorities could be part of that among other factors.

Gaoth Laidir

The trend in tropical activity is actually going down, not up, despite what people say. This is from two prominent tropical scientists, one a forecaster at the NHC.

http://journals.ametsoc.org/doi/full/10.1175/JCLI-D-15-0188.1

4. Conclusions

It was suggested by Klotzbach (2006) and Landsea et al. (2006) that technological improvements during the 1970s and 1980s were primarily responsible for the dramatic increases in the frequency and percentage occurrences of category 4–5 hurricanes worldwide reported in Webster et al. (2005). With 10 additional hurricane seasons now available to analyze, the long-term (1970–2014) trends showed reduced trends in category 4–5 frequency and percentage globally. When restricted to the most recent 25 years (1990–2014) with the most reliable and homogeneous records, the following conclusions are reached from this analysis:

Small, insignificant decreasing trends are present in category 4–5 hurricane frequency in the Northern Hemisphere and globally, while there is no virtually no trend in Southern Hemisphere frequency.
Small, insignificant upward trends are present in category 4–5 hurricane percentage in the Northern Hemisphere, the Southern Hemisphere, and globally.
Large, significant downward trends are present in accumulated cyclone energy in the Northern Hemisphere, the Southern Hemisphere, and globally.

These results provide more evidence that the changes reported by Webster et al. (2005) that occurred in number and percentages of category 4–5 hurricanes globally during the 1970s and 1980s were likely primarily due to improved observational capabilities. These results are more in line with expectations from climate models (Knutson et al. 2010, 2013; Camargo 2013; Christensen et al. 2013; Bender et al. 2010), which suggest that no appreciable change in category 4–5 hurricane numbers or percentages would be detectable at this time due to anthropogenic climate change.
Because of the additional evidence provided here about the artificial impacts of technology on the best-track databases, it is recommended that global studies addressing trends in extreme hurricanes (as well as combined metrics like ACE) begin around 1990. Before this time, the records are currently incomplete and lead to a distorted view of the actual activity that occurred before that time. We would also encourage the further development and extension backward in time of satellite-only homogeneous databases (Kossin et al. 2013) suitable for trend analysis.

Trends in category 4–5 hurricane numbers and percentages and ACE should be revisited whenever historical TC databases are reanalyzed (Hagen et al. 2012) and when another decade or so of additional seasons are recorded. However, given the large natural variability driven by ENSO and other natural phenomena, it is likely to be challenging to confidently ascribe an anthropogenic signal to changes in the most intense tropical cyclones for the next several decades

star gazer

It's important not just to find out what impact a warmer climate and by extension, warm seas, are having on the number and intensity of tropical storms but all the other factors impacting on a tropical storm system so nations affected by them can plan longer term accordingly and warnings are given as early and as accurately as possible. If it happens, a second Category 4 Hurricane making landfall on the US so soon after Harvey would be unusual. No doubt with Harvey, Irma, Jose and Katia there'll be lots of data to add to any potential studies. I would hope that it would be sooner than the next several decades before a clearer picture evolves.

stingray555

Make donations to help the Harvey victims on the Salvation Army website. Payments can be made using paypal.