CoCoRaHS Observers Document Record Tropical Rain from Harvey

There are more than 20,000 CoCoRaHS observers across the U.S., Canada, Puerto Rico, the Bahamas, and the U.S. Virgin Islands. So when a weather disaster occurs, some of our observers are bound to be affected. We have seen that in the past, and it happened again this past week when Harvey slammed into the coast of Texas. Often we don't always know how observers have been affected. Some will post comments with their observations when they get back online or post to the CoCoRaHS Facebook group, and some drop an email to headquarters or their state coordinator let us know their situation. Most of the time, however, we just see the observations disappear from the map.

Texas CoCoRaHS maps for August 24 and August 28, 2017

The comparison might not be obvious at first glance, but there are a lot of gray dots on the August 24 map, and many fewer dots on the August 30 map. The area outlined in yellow is where Harvey came ashore with winds of 120 mph. I looked at the reports from six counties along the coast (Nueces, San Patricio, Aransas, Refugio, Calhoun, and Victoria). On August 24 there were a total of 35 reports submitted for those counties. On August 28, there were only nine. We are all hoping that all of our Texas and Louisiana observers affected by the winds and flooding from Harvey are safe and well.

8/25/2017  TX-VC-39   Getting ready for Harvey. I wont be able to record the rain unfortunately... my gauge is not secure enough to maintain integrity, so I brought it inside. It is now 1:00pm and it has just really started coming down. Pray for me... it's me, my husband and my 88 year old dad, hunkered down in Victoria..I'll be back when the power comes back on.

Further north from landfall,in Harris and surrounding counties, torrential rain and flooding hampered rainfall observations. In some cases the rain came down so hard and fast that observers could not get their gauges before they overflowed (the 4-inch gauge holds approximately 11 inches of rain). We had a few reports of gauges being blown over, and numerous comments about overflowing rain gauges. In places where the flooding was minor observers were able to regularly get out to their gauges and make measurements. Here is an example of a great report from the observer at TX-SJ-12 Oakhurst 3.6 SSE on August 28 detailing his measurements. The total measurement was 16.50 inches, and the comment was as follows:

Measurements and times breakdown: 1.28 was one hour period 7am-8am (8/27/17) 7.84 was 12 hour period 8am-7pm (8/27/17) 7.38 was overnight 7pm (8/27/17)-7am (8/28/17)

Neil Bradley (TX-HRR-116) with
his rain gauge on August 30.

There were 168 Significant Weather Reports submitted by Texas CoCoRaHS observers between August 25 and August 30. All of those were immediately routed to the nearest National Weather Service Office and aided forecasters in their real-time assessment of the storm. One CoCoRaHS observer in Harris County, Neil Bradley (TX-HRR-116, Katy 1.0 NNE) submitted hourly Significant Weather Reports on August 27 and 28. By the time the rain ended on August 29 he had measured 34.52 inches of rain. He also posted regular updates to the CoCoRaHS Facebook group. Greg Story, a meteorologist with the NWS West Gulf River Forecast Center commented "Neil, on behalf of all of us at the NWS West Gulf River Forecast Center, thank you for your timely, invaluable reports. Much appreciated!!"


The rain bands and convective clusters with Harvey resulted in some striking differences in rainfall amounts over short distances. Here is an example showing the bands of rain in the hours after Harvey made landfall. This image is the Storm Total Precip product (radar estimated rainfall) on August 26 at 9:40 a.m. from the Corpus Christi radar.

Radar estimated precip from Corpus Christi radar on 8/26/17 at  9:40 am.
The blue band >10". Sfc reports confirmed 14.46" near Austwell, TX

This is a composite image from three weather radars (Corpus Christi, San Antonio, and Houston) of the storm total precipitation on 8/26 at 2:00 p.m.

Storm Total Precipitation at 2:00 p.m. CDt 8/26/17.
Image is indicating there is already 10"+ west of Houston.

Looking at the colors and pattern is one things, but looking at actual numbers is another. Here is the total rainfall recorded by CoCoRaHS observers over the course of the storm. This only lists amounts greater than 32 inches for Texas and greater than 10 inches for Louisiana, otherwise it would be pages long.

Total precipitation for 8/25/2017-8/31/2017 for Texas and Louisiana

It's no secret the the Houston area is flood-prone, and to monitor conditions in the area the Harris County Flood Control District has automated rain gauges and stream gauges throughout Harris County. With the addition of CoCoRaHS and NWS Cooperative observations the character of precipitation is well captured. The map below is the total precipitation measured by these automatic gauges for through August 29.

Map of precipitation amounts from Harris County Flood Control District rain gauges.
The Cedar Bayou gauge with 51.88 inches is circled in green

This chart shows the 12 hour precipitation amounts measured by the HCFCD rain gauge at Cedar Bayou.

When all was said and done and Harvey finally pulled to the northeast, more than 50 inches of rain had been measured in the Houston area, and more than 45 inches of rain in eastern Texas near Beaumont/Port Arthur. Beaumont, TX received 26 inches of rain in 24 hours Tuesday into Wednesday.

To get some perspective on how incredibly unusual this amount of rain was, check out this map from climatologist Brian Brettschneider.

Hats off to all of our observers in Texas and Louisiana who were able to make measurements through the storm. Thank you for your dedication to CoCoRaHS. There are likely a number of observers who were not able to submit measurements because of wind damage, flood damage, or power outages. We hope you are all safe and that recovery is underway.

Finally, here is the list of precipitation amounts and wind gusts associated with Harvey as compiled by the NWS Weather Prediction Center. This list is long but I wanted to include it before it disappeared from the web.

STORM SUMMARY NUMBER 20 FOR TROPICAL DEPRESSION HARVEY PRELIMINARY
RAINFALL TOTALS AND WIND REPORTS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1000 PM CDT WED AUG 30 2017

...TROPICAL DEPRESSION HARVEY PRELIMINARY OBSERVED RAIN TOTALS AND
WIND REPORTS...

FOR A DETAILED GRAPHICAL DEPICTION OF THE LATEST
WATCHES...WARNINGS AND ADVISORIES...PLEASE SEE WWW.WEATHER.GOV

AT 900 PM CDT...THESE ARE THE MOST RECENT PRELIMINARY RAINFALL AND
WIND REPORTS FROM TROPICAL DEPRESSION HARVEY.  PLEASE REFER TO NHC
FOR THE LATEST PUBLIC ADVISORIES ON HARVEY.

...SELECTED PRELIMINARY STORM TOTAL RAINFALL IN INCHES FROM 800 PM
CDT THU AUG 24 THROUGH 900 PM CDT WED AUG 30...

...ALABAMA...
BONSECOUR                             7.91                   
GASQUE                                7.45                   
GRAND BAY 10.5 NE                     6.81                   
FOLEY 7.4 SW                          6.44                   
ELBERTA                               6.31                   
ORANGE BEACH                          6.03                   
TILLMANS CORNER 4.3 WNW               6.01                   
MOBILE REGIONAL AIRPORT               5.83                   
FAIRHOPE                              5.77                   
GULF SHORES                           5.60                   
MOBILE 11.2 WSW                       5.44                   
MOBILE/BATES FIELD                    5.02                   
SUMMERDALE                            4.73                   
MONTROSE                              4.52                   
DAPHNE 0.4 SW                         4.42                   
FISH RIVER NEAR SILVERHILL 3W         4.35                   
SONNY CALLAHAN ARPT                   4.32                   

...ARKANSAS...
MAMMOTH SPRINGS 2 SSE                 6.42                   

...FLORIDA...
MILTON                                6.92                   
PENSACOLA REGIONAL AIRPORT            6.84                   
UNIVERSITY WEST 2.0 WNW               6.36                   
PACE                                  5.35                   
GULF BREEZE                           5.28                   
ORIOLE BEACH 2 WSW                    3.01                   

...LOUISIANA...
BAYOU CONWAY                         22.25                   
BAYOU TORO NEAR TORO                 20.62                   
KENNER GULLY AT MARK LEBLEU          18.23                   
CALCASIEU RVR AT OLD TOWN BA         18.15                   
W-14 AT JOE SPEARS RD                17.85                   
W-6 AT WARD LINE ROAD                17.24                   
MOSS BLUFF                           16.70                   
BELFIELD DITCH AT BELFIELD ROAD      16.37                   
IOWA 0.9 ESE                         16.36                   
GOLDSMITH CANAL AT GOOS RD           16.02                   
BAYOU ARSENE AT HECKER ROAD          15.84                   
GOLDSMITH CANAL AT HWY 171           15.74                   
LAKE CHARLES 11.5 SSW                15.41                   
RAGLEY 5.0 SE                        15.18                   
EB L-14 AT IOWA BASEBALL FIELD       14.85                   
INDIAN BAYOU AT COFFEY ROAD          14.10                   
TOPSY 4 NNW                          14.08                   
LACASSINE BAYOU AT LORRAIN BRIDGE    13.04                   
ZAVALLA 2 ENE                        12.87                   
SULPHUR 2.2 E                        12.54                   
BON WIER 2 ENE                       12.44                   
HACKBERRY 5 SSE                      12.33                   
CONTRABAND BAYOU AT 18TH STREET      12.28                   
WELSH 0.7 W                          12.26                   
W-4 AT NELSON ROAD                   12.12                   
GILLIS 4 WSW                         12.11                   
FORT POLK                            11.96                   
BUXTON CREEK AT DOUGLAS ROAD         11.21                   
CHOUPIQUE BAYOU AT HWY 90            11.02                   
LACASSINE NATIONAL 2 ENE             10.55                   
BAYOU DINDE AT PICARD ST              9.76                   
LEBLEU SETTLEMENT 2 WNW               9.64                   
FORKED ISLAND 5 ENE                   9.37                   
BUNDICK CREEK NEAR DE RIDDER          9.26                   
PECAN ISLAND 2 E                      9.14                   
LAKE CHARLES MUNI ARPT                9.08                   
NEW IBERIA/ACADIANA                   8.92                   
VERNON - FTS                          8.77                   
LAFAYETTE RGNL ARPT                   7.14                   
NEW ORLEANS/MOISANT                   5.88                   
NEW ORLEANS/LAKEFRONT                 5.33                   
ENGLAND AFB/ALEXANDRIA                4.84                   
SLIDELL AIRPORT                       3.82                   
BATON ROUGE/RYAN MUNI ARPT            3.17                   

...MISSISSIPPI...
GAUTIER                               8.27                   
SANDHILL CRANE - FTS                  7.90                   
GRAND BAY                             6.06                   
OCEAN SPRINGS 3.6 ESE                 4.61                   
MOSS POINT - TRENT LOTT INTL ARPT     4.55                   
PASCAGOULA                            4.52                   
PEARLINGTON 4.4 N                     3.99                   
JOURDAN RIVER NEAR KILN               3.35                   
TANGIPAHOA RIVER AT OSYKA             3.15                   
TYLERTOWN 9 WNW                       3.08                   
NATCHEZ/HARDY                         2.91                   
KEESLER AFB/BILOXI                    2.55                   

...TEXAS...
CEDAR BAYOU AT FM 1942               51.88                   
CLEAR CREEK AT I-45                  49.40                   
DAYTON 0.2 E                         49.23                   
MARYS CREEK AT WINDING ROAD          49.20                   
BEAUMONT/PORT ARTHUR                 47.35                   
SANTA FE 0.7 S                       46.70                   
PASADENA 4.4 WNW                     45.74                   
HORSEPEN CREEK AT BAY AREA BLVD      45.60                   
SOUTH HOUSTON 4.0 SSW                44.91                   
BERRY BAYOU AT FOREST OAKS BLVD      44.80                   
BERRY BAYOU AT NEVADA                44.44                   
FRIENDSWOOD 2.5 NNE                  44.05                   
LITTLE VINCE BAYOU AT BURKE RD       43.52                   
HOUSTON WEATHER FORECAST OFFICE      43.38                   
LEAGUE CITY 2.7 NE                   43.32                   
WEBSTER 0.4 NW                       43.32                   
LNVA CHEEK CANAL AT DITCH 407        43.11                   
LITTLE CEDAR BAYOU AT 8TH ST         42.32                   
ARMAND BAYOU AT GENOA-RED BLUFF RD   42.16                   
TURKEY CREEK AT FM 1959              42.12                   
BOONDOCKS RD AT TAYLORS BA           41.86                   
ARMAND BAYOU AT PASADENA LAKE        41.20                   
TAYLOR LAKE AT NASA ROAD 1           40.44                   
SH 124 AT HILLEBRANDT BAYOU          38.18                   
MAHAW BAYOU AT ENGLIN RD             37.75                   
JACINTO CITY                         37.60                   
HUNTING BAYOU AT LOOP 610 EAST       37.00                   
TELEPSEN                             36.60                   
MAHAW BAYOU AT BRUSH ISLAND ROAD     36.53                   
FIRST COLONY 4 WSW                   36.34                   
BEAMER DITCH HUGHES RD               36.32                   
LA PORTE 1 N                         36.24                   
BAYTOWN 2 NW                         35.64                   
MOUNT HOUSTON                        35.60                   
HOUSTON/CLOVER FIELD                 33.37                   
HOUSTON/INTERCONTINENTAL             31.26                   
KATY 6 NE                            31.23                   
HOUSTON/WILL HOBBY                   27.88                   
HOUSTON/D.W. HOOKS                   27.01                   
GALVESTON/SCHOLES                    22.84                   
COLLEGE STATION 2 SSW                19.64                   
VICTORIA 3.8 NW                      15.60                   
AUSTIN 4 SSE                         10.28                   
AUSTIN/MUELLER MUNI ARPT             10.07                   
CORPUS CHRISTI 3.6 S                  6.23                   

...SELECTED PEAK WIND GUSTS IN MILES PER HOUR EARLIER IN THE
EVENT...

...TEXAS...
PORT ARANSAS 2 ENE                   132                   
COPANO VILLAGE 1 ENE                 125                   
LAMAR 2 SSW                          110                   
ROCKPORT 1 S                         108                   
TAFT 5 NNE                            90                   
MAGNOLIA BEACH 8 ESE                  79                   
EDNA                                  73                   
FLOUR BLUFF 4 ESE                     72                   
ARANSAS PASS 7 SE                     71                   
CLEAR LAKE SHORES 1 WSW               71                   
BRAZOS 451                            70                   
PALACIOS MUNICIPAL AIRPORT            69                   
CORPUS CHRISTI NAS 5 SE               65                   
GANADO 7 S                            64                   
LA WARD                               64                   
BAYOU VISTA 13 E                      61                   
NEW BRAUNFELS MUNICIPAL AIRPORT       58                   
QUINTANA 1 NE                         58                   
SUGAR LAND MUNICIPAL AIRPORT          58                   
JONES CREEK 9 SW                      55                   
LA MARQUE 2 E                         55                   
FREEPORT 1 ESE                        54                   
SAN LEON 19 E                         54                   
MISSOURI CITY 1 SE                    53                   
SAN ANTONIO INTL ARPT                 53                   
WEBSTER                               53                   
BERGSTROM INTL AIRPORT                52                   
GONZALES AIRPORT                      52                   
NASSAU BAY                            52                   
TEXAS CITY 4 ENE                      52                   


THIS WILL BE THE FINAL STORM SUMMARY ON RAINFALL AND WINDS
ASSOCIATED WITH HARVEY. WPC WILL CONTINUE TO COMPILE OBSERVATIONS
ASSOCIATED WITH THE REMNANTS OF HARVEY IN UPCOMING PUBLIC
ADVISORIES (TCPAT4/WMO HEADER WTNT33 KWNH) COMMENCING WITH THE
NEXT SCHEDULED TCPAT4 AT 0900Z/400 CDT. THESE ADVISORIES WILL
STILL BE AVAILABLE AT WWW.WPC.NCEP.NOAA.GOV.

THIS WILL BE THE LAST STORM SUMMARY ISSUED BY THE WEATHER
PREDICTION CENTER FOR THIS EVENT. PLEASE REFER TO YOUR LOCAL
NATIONAL WEATHER SERVICE OFFICE FOR ADDITIONAL INFORMATION.

SANTORELLI

A Brief History of Harvey

"Local rainfall amounts of 50 inches would exceed any previous Texas rainfall record. The breadth and intensity of this rainfall are beyond anything experienced before. Catastrophic flooding is now underway and expected to continue for days."

 NWS Weather Prediction Center, Sunday, August 27

Harvey started out as a rather innocuous disturbance in the Caribbean more than 10 days ago. It was disorganized and at times looked like it was going to fall apart. On Thursday, August 17 the disturbance was promoted to Tropical Storm Harvey. By late on Saturday August 19 Harvey had weakened into a tropical wave. There were no advisories issued Sunday through Tuesday as what was left of Harvey drifted west. On Wednesday, August 23  a Hurricane Hunter found that Harvey had regenerated in the Bay of Campeche, and advisories were issued. At that time Harvey was expected to make landfall along the southern Texas coast by Saturday morning. It was also expected that Harvey might slow down or stall out over southeast Texas,

Harvey intensified quickly on Thursday morning and was forecast to become a hurricane before landfall. By early afternoon on Thursday the storm had become Hurricane Harvey, with further intensification expected. By midnight Harvey was a Category 2 storm with winds near 100 mph. In the 4:00 a.m. advisory on Friday the National Hurricane Center expected further intensification and expected Harvey wander slowly through southeast Texas for the next five days. It also included this statement:

"Devastating and life-threatening flooding is expected across the middle and upper Texas coast from heavy rainfall of 15 to 25 inches, with isolated amounts as high as 35 inches, from today through next
Wednesday."

The 4:00 p.m. advisory on Friday indicated Harvey's winds had increased to 125 mph, and by 7:00 p.m. Harvey was a category 4 storm with winds of 130 mph. Hurricane Harvey made landfall just before 10:00 p.m. CDT on the Texas coast over the northern end of San Jose Island about 4 miles east of Rockport. The storm stalled about 60 miles east of San Antonio for awhile, then gradually drifted southeast back into the Gulf of Mexico. Early this morning (August 30), Harvey made landfall for a second time just west of Cameron, Louisiana. The excellent graphic below shows Harvey's travel from the Atlantic to this morning's second landfall.

The path of Hurricane Harvey.
Credit: Brandon Moses (via Twitter)

Josh Morgerman (@iCyclone), a hurricane chaser, was in Rockport, TX when Harvey made landfall. You can read his interesting account of his "chase" of Harvey at this link.

 Initially the high winds and storm surge were the focus of attention. The Texas coast from Rockport to Port Aransas was raked by 100+ mph winds, and storm surge quickly flooded coastal areas. As Harvey drifted inland the winds weakened, but the worst of the storm was starting to take shape.

This is the  storm relative velocity image (SRV) out of Corpus Christi radar at 4:10 p.m. CDT on Friday, August 25. Max winds outbound ~140 mph (brown), inbound ~115 mph (blue).

With a few exceptions (Hurricane Andrew, for one) winds usually aren't the worst of a hurricane or tropical storm. Torrential rain and resultant flooding (as well as flooding from storm surge) usually result in the most damage. As Harvey moved ashore late on Friday feeder rain bands on the east side of the storm were starting what was to be an epic and unprecedented tropical rain event. The astounding forecasts of up to 50 inches of rain verified by Tuesday afternoon. Though the rain ended in Houston, it was unrelenting in eastern Texas and western Louisiana. 26 inches of rain fell in 24 hours in Beaumont, TX, and radar estimated rainfall as of early afternoon today was in excess of 50 inches there as well.

Radar estimated rainfall from the Lake Charles, LA radar at 10:50 a.m. CDT Wednesday, August 30. Rain continued for several hours after this image. Max value indicated by radar was 50.80". The white to gray shading is 40 to 50 inches.

Tonight Harvey was downgraded to a tropical depression. The storm is expected to continue moving northeast and into Ohio by Saturday.producing heavy rain in the Tennessee and Ohio Valleys and south.

Next post: CoCoRaHS Observers, Rainfall, and Hurricane Harvey