August 2017: Looking Back at Harvey 5 Year Later

[srainhoutx]

Tuesday afternoon briefing from Jeff:


***Hurricane landfall along the TX coast increasing likely Friday or Saturday***

Review hurricane response plans and be fully prepared to enact those plans starting tomorrow.

Discussion:
Satellite images show an increasingly well defined surface circulation across the NW Yucatan currently that will be moving over the southern Gulf of Mexico in the next several hours. The system currently lacks any deep convection near the center with thunderstorms currently displaced to the north along the northern coast of the Yucatan. The circulation is moving toward the NW around 10-12mph and this motion is expected to continue.

Track:
There has been little change in the forecast track reasoning today with a general NW track toward the TX coast expected Wed-Fri. Major global models continue to be in decent agreement moving Harvey into a weakness over the TX coast between a building ridge of high pressure over the SW US and high pressure over the SE US and a trough across the Great Lakes. Landfall locations continue to shift around with each model run, but the main consensus continues to be in the region between Corpus Christi and Matagorda Bay.

The steering flow nearly collapses as Harvey reaches the coast and expect a decrease in forward speed as the system moves inland over the coastal bend on Friday night. This is where the forecast becomes greatly complicated as Harvey becomes trapped in a weak steering regime across SC/SE TX into the early portion of next week. The system is effectively left to meander and loop somewhere in the region bounded by Matagorda Bay, Austin, and Galveston. Eventually it appears Harvey will slowly track E to ENE either along the coast or inland of the coast across SE TX Saturday-Tuesday.

Intensity:
Conditions appear favorable for intensification of Harvey up to landfall on the TX coast. All parameters appear to be satisfied including warm SST’s, 200mb high pressure over the center of the system, potential dual outflow channels to the NE and SW of the center. It is possible that a period of rapid intensification could occur as Harvey nears the middle TX coast on Friday. Intensity forecast skills are poor especially when dealing with rapid intensification…this aspect will need to be monitored closely over on Thursday and Friday as Harvey approaches. Current coordinated NHC/WPC positions bring s minimal hurricane into the coast in the reach between Corpus and Port O Connor Friday evening.

Impacts:
Without any sort of NHC track guidance the following impacts are based on the TCVN (consensus model track) with storm surge forecast off ET surge, but I have cut it back some based on the latest GFS run. Have also taken a good look at the cat 1 SLOSH output for a NW tracking hurricane into just W of Matagorda Bay and merging those values with ET surge seems to be a good compromise at the moment. Additionally, there has been some coordination with the storm surge unit at NHC via the local WFO today. Rainfall has been coordinated with local WFO’s and WPC…mainly to encourage WPC to raise expected totals.

Rainfall:
I have never seen the GFS and ECWMF models forecasting such a large amount of rainfall over such a large area. Widespread rainfall amounts of 8-12 inches is likely with isolated totals of 20 inches or more. River, creek, bayou, and flash flooding would be a given with totals of this magnitude. Unlike so many of the flood events we deal with across this area where isolated areas get the very high totals…the potential here is for a very large area to see excessive amounts of rainfall.

Widespread: 8-12 inches (all areas)

Isolated: 20 inches +

Storm Surge:
Will start to see increasing tides Thursday afternoon and possible we may hit 3.0 ft total water level Thursday afternoon/evening especially Matagorda Bay southward toward Mustang Island. Will go with total water levels Friday rising to 4.0-5.0 feet along all of the upper and middle coast and likely nearing 6.0 feet around Matagorda Bay. 4.5 feet is our critical warning threshold along much of the upper coast for the start of impacts and think we will hit those levels on Friday especially Matagorda Bay. Overwash and coastal flooding appears likely Friday from Palacios southward including Matagorda Island and along the west side of Matagorda Bay.

Tides will increase Friday night across the coast NE of Palacios as SE winds pile water and wave action onto the coast. Will build to 4.0-5.5 feet Friday night along Brazoria, Galveston, and SE Harris coast with overwash likely on the west end of Galveston and Bolivar. With the continued onshore flow well into Saturday and Sunday tides will only worsen over the weekend as water becomes trapped in the bays…especially the western side of Galveston Bay. Certainly looking at potential coastal flooding around Clear Lake, Kemah, Seabrook, Galveston Island, Bolivar on Saturday…but don’t want to go much more than 5.5-6.0 feet total water level at this time as a lot of factors are in play.

Matagorda Bay: 4-5 ft (Friday/Saturday)

Galveston Bay: 4-5 ft (late Friday/Saturday)

Gulf Beaches: 4.5-5.5 ft (Friday/Saturday)

Onset of 3.0 ft total water level rise Thursday afternoon/evening

Winds:
A lot of uncertainty with this aspect.

Tropical storm conditions (40mph sustained) will begin to reach the middle coast on Friday around midday and spread inland into the evening hours. Will bring Jackson, Matagorda, Calhoun, and Wharton Counties into the TS force winds by Friday evening and build to hurricane force (75mph sustained) over Calhoun County southward to near Corpus Friday night. Could be very near hurricane conditions into much of Matagorda Bay Friday night and possibly Matagorda County with tropical storm conditions up to Galveston by Saturday morning. If the system does in fact turn NE/ENE just inland this will bring tropical storm and potential hurricane conditions across a larger portion of SE TX.

Should get better details on this tomorrow if NHC starts advisories.

Actions:
Hurricane plans should be fully prepared to be enacted on Wednesday including fully stocked hurricane kits.

Ride out teams should be notified and activation of COOP’s is recommended starting Wednesday.

Preparations should include the potential for loss of power and prolonged excessive rainfall and flooding along with prolonged high coastal tides. Some areas near the coast may become cut-off as early as Friday.

Significant rises on area rivers, creeks, and bayous is a real threat and residents living in flood prone areas should be prepared for rising water and potentially significant flooding.

Note:
GIV upper air mission is underway over the Gulf of Mexico which should help firm up model guidance for the 12Z runs on Wednesday…some of the samples may get into the 00Z runs this evening.

USAF/NHC have several C-130 53rd missions planned into Harvey starting tomorrow and this will continue up to landfall…so there will be nearly constant checking on intensity trends.

Tropical storm, hurricane, and storm surge watches and/or warnings may be required for portions of the TX coast on Wednesday

[Andrew]

I would definitely start getting early precautions ready. Pickup up extra water, filling up on gas and having emergency plans in place will be a good idea. Models still have a wide degree of uncertainty for intensity but one thing looks pretty certain and that is a lot of rain. What is the most concerning is the amount of the surface area that could be impacted. Models show most of SE Texas receiving 7-10 inches and it could be much much more. Now that the weak surface low is exiting the Yucatan Peninsula we can monitor where a surface low develops and have a better idea where it will go.

[unome]

recon http://hurricanecity.com/recon/

Jim hosts tropicalatlantic.com's to help reduce the load on Chris' site - the Cesium mapper is awesome, with no plugin required: http://hurricanecity.com/recon/recon.cg ... ing=cesium

with recon through 5:27pm EDT - Red "X" was 2pm NHC Atlantic outlook position:

http://imgur.com/ZKbSNWx

[davidiowx]

Some strong wording there by Jeff. This is going to be very interesting. Late tonight through tomorrow will be important in regards to advisories, path, etc.

[sau27]

Another concern will be how the position of the circulation affects drainage out of the bayous. If it sits just west or southwest of here it will continue pushing water in towards the bay all while dumping tons of rain.

[Scott747]

12z euro and 18z gfs are strikingly similar through hr 144.

[srainhoutx]

12z euro and 18z gfs are strikingly similar through hr 144.

Still dealing with Harvey at 168 along Matagorda and Brazoria Counties. Prolific rainfall totals above 24 inches in some locations.

[Andrew]

GFS showed 30 to up to 40inches over Galveston. 10-15 inches over Harris county. Good news is it is weaker during landfall. Still, the biggest concern looks to be rain and maybe some weak storm surge.

[Scott747]

12z euro and 18z gfs are strikingly similar through hr 144.

Still dealing with Harvey at 168 along Matagorda and Brazoria Counties. Prolific rainfall totals above 24 inches in some locations.

Combined with what it does once back in the Gulf, it's one of those jaw dropping runs. Especially since we're getting into a window where these solutions are viable with the big two (gfs and euro) in so much agreement.

Hopefully there are some changes in the 5+ day range.....

[srainhoutx]

TropicsWatch‏ @TropicsWatch · 33m33 minutes ago
Our latest ensembles-based #TRAC guidance indicates a high chance of a lower to middle TX coast hit from #Harvey. Very heavy rain potential.

08222017 TropicsWatch DH3crjAVYAAJcPx.jpg

[TexasBreeze]

I don't think I have seen models forecasting this kind of rainfall and agree with each other about the extreme amounts before!!!

[ticka1]

i didnt wait -water and food stuff purchased. Gas tomorrow and extra for generator. what timeframe we looking at all this happening?

[unome]

cool tool found on West Gulf River Forecast Center's site https://www.weather.gov/wgrfc/

https://noaa.maps.arcgis.com/apps/webap ... d980555528

[srainhoutx]

i didnt wait -water and food stuff purchased. Gas tomorrow and extra for generator. what timeframe we looking at all this happening?

Looks like Friday night throughout the weekend into Monday, possibly extending into Tuesday depending on the final verdict.

[ticka1]

i didnt wait -water and food stuff purchased. Gas tomorrow and extra for generator. what timeframe we looking at all this happening?

Looks like Friday night throughout the weekend into Monday, possibly extending into Tuesday depending on the final verdict.

thank you - hope not until late friday night

[stormlover]

https://www.tropicaltidbits.com/analysi ... 0&ypos=170

navy run

[unome]

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 PM EDT Tue Aug 22 2017

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

Satellite images and surface observations indicate that the area of low pressure associated with the remnants of Harvey is moving off the coast of the Yucatan Peninsula into the southern Gulf of Mexico. Environmental conditions are conducive for a tropical depression or tropical storm to form on Wednesday or Thursday while the low moves northwestward at about 10 mph across the western Gulf of Mexico, possibly reaching the northwestern Gulf coast on Friday. Regardless of development, this system is likely to slow down once it reaches the coast, increasing the threat of a prolonged period of heavy rainfall and flooding across portions of Texas, southwestern Louisiana, and northeastern Mexico into early next week. This system could also produce storm surge and tropical storm or hurricane force winds along portions of the Texas coast later this week, and interests from northeastern Mexico to southwestern Louisiana should continue to monitor its progress. Please refer to products from your local National Weather Service office for more information on this system.
* Formation chance through 48 hours...high...90 percent.
* Formation chance through 5 days...high...near 100 percent.

A large area of disorganized showers and thunderstorms stretching across the Bahamas, Florida, and the adjacent waters is associated with a trough of low pressure. Any development of this system during the next few days should be slow to occur while it drifts northward over Florida and the adjacent waters. Environmental conditions could become a little more conducive for tropical or subtropical development by the weekend when the system begins to move northeastward over the western Atlantic. Regardless of development, very heavy rain and flooding is possible over portions of the Florida peninsula during the next few days. Please refer to products from your local National Weather Service office for more information on this system.
* Formation chance through 48 hours...low...10 percent.
* Formation chance through 5 days...low...30 percent.

$$
Forecaster Berg

[unome]

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
756 PM EDT Tue Aug 22 2017

Tropical Weather Discussion for North America, Central America Gulf of Mexico, Caribbean Sea, northern sections of South America, and Atlantic Ocean to the African coast from the Equator to 32N. The following information is based on satellite imagery, weather observations, radar and meteorological analysis.

Based on 1800 UTC surface analysis and satellite imagery through 2315 UTC.

...SPECIAL FEATURES...
A tropical wave extends from 25N89W to 16N90W moving NW at 10-15 kt. The remnant circulation of Harvey continues to be analyzed as a 1010 mb low pressure along the wave axis, over the Yucatan Peninsula near 20N90W, with scattered to numerous showers and thunderstorms occuring from 20N-26N between 85W-91W, including the Yucatan Channel where numerous showers and tstms are currently noted. The low pressure area (remnants of Harvey) is forecast to emerge off the coast of the Yucatan Peninsula tonight. Environmental conditions are conducive for a tropical depression or tropical storm to form on Wednesday or Thursday while the low moves northwestward at about 10 mph across the western Gulf of Mexico, possibly reaching the northwestern Gulf coast on Friday. Regardless of development, this system is likely to slow down once it reaches the coast, increasing the threat of a prolonged period of heavy rainfall and flooding across portions of Texas, southwestern Louisiana, and northeastern Mexico into early next week. This system could also produce storm surge and tropical storm or hurricane force winds along portions of the Texas coast later this week, and interests from northeastern Mexico to southwestern Louisiana should continue to monitor its progress. A gale warning has been issued for the SW and west-central Gulf beginning Wednesday morning. See latest NWS High Seas Forecast under AWIPS/WMO headers MIAHSFAT2/FZNT02 KNHC and the Tropical Weather Outlook under AWIPS/WMO headers MIATWOAT/ABNT20 KNHC for more details.

...TROPICAL WAVES...
A tropical wave extends from 23N29W to a 1011 mb low pressure within the monsoon trough located near 14N34W moving W at 15-20 kt. Satellite imagery indicates a large area of cloudiness in association with this wave, but convection is limited. A cyclonic turning is seen near 18N33W. This wave remains in a very moist area based on TPW imagery and has a well pronounced 700 mb trough.

A tropical wave is moving across the eastern Caribbean and extends from 17N73W across Colombia to near 08N74W moving W at 20-25 kt. An area of showers with embedded tstms is noted near the northern end of the wave axis from 15N-17N between 70W-73W. The wave is also enhancing some shower and tstm activity over northern Colombia. The wave coincides with a 700 mb trough, and is well depicted in the moisture product. This system will move across the central Caribbean through mid week, and across the western Caribbean later in the week.

...ITCZ/MONSOON TROUGH...
The monsoon trough extends from the African coast near 14N17W to 17N25W, then resumes near 14N34W to 10N40W to 08N51W. The Intertropical Convergence Zone axis continues from 08N51W to 10N57W. Scattered moderate isolated strong convection is from 09N-14N E of 20W. A large cluster of moderate to strong convection is approaching the west coast of Africa likely associated with the next tropical wave. Scattered moderate convection is within about 150 nm SE of a line from 15N29W to 10N37W, and within 75 nm south of trough axis between 45W-49W.

...DISCUSSION...

GULF OF MEXICO...
Attention remains focused on the remnant circulation of Harvey currently located over the Yucatan Peninsula. Please, see Special Features section for details. The large and well defined upper-level low that was affecting the Gulf waters with showers and tstms during the previous days has weakened some and now a large anticyclonic circulation has developed over the eastern Gulf. The upper-level low is still spinning over the NW Gulf near 27N93W producing isolated showers and tstms. A 1020 mb high pressure centered near Mobile, Alabama extends a ridge over the northern Gulf producing mainly gentle winds.

CARIBBEAN SEA...
A tropical wave is moving across the Caribbean Sea. Please, see Tropical Waves section for details. The most recent scatterometer data provide observations of fresh to locally strong SE winds across the NW Caribbean mainly N of 20N W of 83W. Similar wind speeds are noted over the central Caribbean. Strong trade winds are forecast to pulse off the coasts of northeast Colombia and northwest Venezuela in the wake of the tropical wave currently located along 73W/74W. A surface trough over the Atlantic extends to near Martinique in the Windward Islands producing isolated showers. Moisture associated with this trough will affect mainly the Leeward Islands later tonight and Wednesday, reaching the UK/US Virgin Islands by Wednesday night. This will increase the chance for showers with isolated tstms across the islands.

...HISPANIOLA...
Scattered showers with embedded tstms are observed this evening over Hispaniola, more concentrated over Haiti. Daytime heating, local sea breezes and mountain upslope lifting will continue to combine with available moisture to produce isolated to scattered showers and thunderstorms mainly during the afternoon and evening hours.

ATLANTIC OCEAN...
A trough of low pressure persists between the NW Bahamas and Florida producing a large and disorganized area of showers and thunderstorms. The trough extends from 29N79W across south Florida to the Florida Keys. Any development of this system during the next few days should be slow to occur while it drifts northward over Florida and the adjacent waters. Environmental conditions could become a little more conducive for tropical or subtropical development by the weekend when the system begins to move northeastward over the western Atlantic. Regardless of development, very heavy rain and flooding is possible over portions of the Florida peninsula during the next few days. Farther east, there is another surface trough that extends 27N57W to 19N57W to near Martinique in the Windward Islands. This trough is likely the surface reflection of an upper- level low located near 27N58W. An earlier scatterometer pass showed the wind shift associated with this trough. The upper-level low is generating isolated showers and tstms mainly from 22N-31N between 53W-60W. The remainder of the Atlantic forecast area is under the influence of the subtropical ridge.

For additional information please visit
http://www.hurricanes.gov/marine

$$
GR

[TexasBreeze]

Deep convection is starting to erupt just off the northern Yucatan coast. Looks like all systems go...

[srainhoutx]

00Z update shows Harvey in the Southern Gulf. Early track and intensity guidance. Good night folks. Long days ahead it appears.