TEXAS CoCoRaHS OBSERVER AISD Summer 2017 ―Because every drop counts, as do all Zeros.‖ Welcome to the Hurricane Harvey sets new rain records Texas CoCoRaHS By John Nielsen-Gammon, Observer newsletter. The purpose of this newsletter Texas State Climatologist, Texas is to keep observers informed A&M University of the latest news, events and happenings related to the Co- Was there weather this sum- CoRaHS program here in Texas, as well as news about mer in Texas before Hurricane Harvey? the latest weather patterns It's hard to remember anymore. affecting each region of Texas. Harvey didn't set the record for If you have questions, greatest total rainfall production in comments or suggestions, feel free to contact us via the Texas by a single storm. It ranks third emails listed on the back page. on that list, behind storms in late De- cember 1991 and late October 2015. It also didn't set the record for greatest Expanded coverage single-day rainfall total. That record is of Hurricane still held by Alvin, Texas, with 42" dur- Harvey throughout ing Tropical Storm Claudette in 1979. this newsletter Otherwise, it seems that Harvey is king. Downtown Houston just flooded all around." Among CoCoRaHS observers, writes Christian Tycksen (@ctycksen) on In- the highest storm total observation was stagram (KHOU.COM) Inside this issue: 49.31", which is a partial estimate be- cause the rain gauge overflowed when Hurricane Harvey about a foot and a half of water fell slams Texas 1 during one 24-hour period. This total Flying into Hurricane exceeds the single-storm contiguous Harvey 16 United States record for a single tropi- cal storm of 48", which of course was Importance of Co- CoRaHS Reports 23 also recorded in Texas (from Tropical during flood events Storm Amelia in 1978). A few other gauges in southeast Texas recorded Sending Significant Weather Reports 27 higher values. Those gauge totals are still being validated, but it does seem Summer Climate that a CoCoRaHS observation will not Summary for RGV 34 be the new record. Too bad we didn't have a volunteer in the right (or Fall Weather Outlook 42 wrong) place! `For flood purposes, what matters is Houston’s Southwest Freeway (Interstate 69) CoCoRaHS Weather not rainfall at a single location but at McGowen St. underwater due to Hurri- Talk Scxhedule 44 CONTINUED ON PAGE 2————> cane Harvey’s heavy rainfall. Page 2 Summer 2017 Texas CoCoRaHS Observer Hurricane Harvey sets new rain records FROM PAGE 1—>rainfall over a given area during a given period of time. At this early stage in the analysis, it appears that Harvey broke all known United States re- cords for rainfall accumulation over a broad area for three or more days. In many cases, the records were not merely broken, they were crumpled, shattered, dropped on the floor, swept into a pile, scooped up, and tossed into the trash can. The first figure (at right) shows the United States record av- erage rainfall accumulation over 10,000 square miles over a 5-day period. Previously, the 20" mark had barely been broken twice. Harvey produced well over 30", ex- ceeding the previous record by over 50%. As you can see, records go back quite a long ways, though eight of the eleven events listed occurred during the past 25 years. The second figure compares the rainfall accumulation in Harvey over Harris County, Texas (home of Houston and some surrounding suburbs; size 1,777 square miles) with the greatest rainfall totals over similarly-sized areas ever observed in the United States. The message here is that if you took the wettest storm ever recorded in United States history over an area the size of Harris County, and moved and rearranged it so that the absolute wettest part of the storm was per- fectly targeted onto Harris County, it still wouldn't have produced as much rain there as Harvey pro- duced. Outside my office I now have a stack of five CoCoRaHS rain gauges, because that's apparently what you need now if you want to measure a Texas rainstorm. Texas CoCoRaHS Observer Summer 2017 Page 3 First major hurricane since 1970 strikes Coastal Bend By National Weather Service Depression Harvey reformed. Initially, NHC believed Harvey would WFO Corpus Christi become either a strong tropical storm or a Category 1 hurricane Hurricane Harvey is the first Major Hurricane to strike before making landfall somewhere between Brownsville (early Fri- South Texas since Celia in 1970...and first Hurricane to day morning) and Houston (early Saturday morning), with the most strike the Texas Coast since Ike in 2008... likely location near the Rockport area late Friday night . However, Over the past several years, meteorologists in with wind shear in the Western Gulf of Mexico weakening, Tropical South Texas (and other areas) have stated "it's not a Storm Harvey was intensifying quickly. By Wednesday evening, Har- matter of if but when" a major hurricane would strike vey was forecast to make landfall as a hurricane somewhere over the Middle Texas Coast. The last hurricane to do so was the Texas Coast. th Celia back on August 3rd, 1970. Well, the "when" hap- On Thursday August 24 , Harvey's impact on the Mid- pened on August 25th 2017, when Harvey made landfall dle and Upper Texas Coast seemed almost certain and poten- along the Middle Texas Coast. Harvey exploded rapidly tially devastating. Not only was Harvey forecast to become a from a tropical depression to a major hurricane in less hurricane by Thursday evening, but it was expected to than 36 hours. After impacting the Yucatan Peninsula strengthen and make landfall as a major hurricane (Category earlier in the month as a tropical storm, Harvey moved 3 or higher) on Friday (see forecast). Worse yet, once the into the warm waters of the Gulf of Mexico late on Tues- storm moved inland, it was forecast to eventually stall and day August 22nd. Below is a summary of Harvey's lifecy- meander over South or Southeast Texas for days. Thus, Major High water on Houston’s South Freeway (SH 288) at Calumet St overpass. cle. hurricane Harvey was not only forecast to produce devastating The birth of Harvey occurred on Sunday August winds, but extremely heavy and excessive rainfall, producing (from Houston Chronicle) 13th, 2017 as a tropical wave emerged off the west coast of devastating and historic flooding over areas especially east of Africa, eventually merging with a broad area of low pressure the center of circulation (still most likely just north of Copano near the Cabo Verde Islands. At first, it was thought the Bay). wave and the low pressure area would have a more west- Harvey underwent rapid intensification and quickly northwest track, threatening the Lesser Antilles. However, became a Category 3 hurricane on Friday at 2 PM (120 mph this low stayed more on a westward course as it moved over sustained winds) and then a Category 4 hurricane (130 mph the open Atlantic Ocean toward the Eastern Caribbean Sea. sustained winds) early Friday evening. As Harvey slowly ap- For a few days on its westward track, "Harvey" remained proached the coast, the National Weather Service in Corpus disorganized, and there was some uncertainty whether the Christi issued a rare Extreme Wind Warning. Extreme wind low would become a tropical cyclone. However, by Thursday CONTINUED PAGE 4———-> August 17th, the National Hurricane Center began issuing advisories and forecasts on Tropical Cyclone Nine Thursday morning, and Tropical Storm Harvey Thursday afternoon. Tropical Storm Warnings were issued that after- noon for Martinique, St. Lucia, Barba- dos, and St. Vincent and the Grenadines. Tropical Storm Harvey impacted the Windward Islands on Friday, August 18th, entering the Eastern Caribbean Sea as a minimal tropical storm, and eventu- ally weakening to a tropical wave late Saturday evening. Although there was some potential for the remnants of Har- vey to reorganize into a tropical cy- clone, a tropical cyclone failed to form as the remnants of Harvey moved into the Yucatan Peninsula on Tuesday morning, August 22nd. With very warm waters in the Bay of Campeche and the Western Gulf of Mexico, the National Hurricane Cen- ter (NHC) was fairly confident that the remnants of Harvey would reform into Hurricane Harvey caused significant damage to many structures in Rockport, a tropical cyclone. At 10 AM CDT as well as much of the Texas Coastal Bend. Wednesday August 23rd, Tropical Page 4 Summer 2017 Texas CoCoRaHS Observer Hurricane Harvey—Corpus Christi Region FROM PAGE 3——>warnings are issued businesses lost power for days, with producing catastrophic devastating for landfalling major hurricanes with the hardest hit areas likely losing and deadly flash and river flooding. winds of 115 mph or higher. Harvey was power for several weeks. Although Southeast Texas beared the brunt of forecast to have winds in the eyewall there was a significant number of the heavy rainfall, with some areas between 115 and 130 mph! Three ex- trees, fences and power poles down or receiving more than 40 inches of rain treme wind warnings were ultimately damaged in the Corpus Christi Metro- in less than 48 hours! Cedar Bayou issued for Harvey. The eye of Major Hur- politan area, structural damage was in Houston received a storm total of ricane Harvey first made landfall on San much more isolated. 51.88 inches of rainfall which is a Jose Island and then near the Rockport The storm surge from Harvey new North American record. How- and Fulton, Texas area at around 10 PM brought dramatically increased water ever, South Texas residents were not CDT.