November 18, 2019

Slow-moving Tropical Depression Imelda brings over 30 inches of rain to Texas

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By Bob Henson From Weather Underground

A man walks into high water into his neighborhood as rain from Tropical Depression Imelda inundated the area on Thursday, Sept. 19, 2019, near Patton Village, Texas, about 30 miles northeast of Houston. Image credit: Brett Coomer/Houston Chronicle via AP.

Devastating flooding unfolded across far southeast Texas late Wednesday night and spread into the Houston area on Thursday morning, as Tropical Depression Imelda continued to plague the region. At 11 am EDT Thursday, Tropical Depression Imelda was located about 50 miles north of Houston, moving north to northwest at 3 – 6 mph. The depression brought a band of intense thunderstorms between Houston and Beaumont that held nearly stationary for hours on end, dumping prodigious amounts of rain. Doppler radar detected winds of up to 56 mph just above ground level pushing massive amounts of moisture from the Gulf of Mexico into the thunderstorms. Rainfall of 3-5” per hour was falling atop ground already saturated by days of heavy rain.

Figure 1. Infrared image of the thunderstorm complex locked over southeast Texas at 1602Z (12:02 pm EDT) Thursday, September 19, 2019. Image credit: tropicaltidbits.com.

Several flash flood emergencies were in effect across far southeast Texas late Thursday morning, including large parts of Houston and Harris County. Water has entered hundreds of homes, and more than 1000 people have called for rescues, according to Beaumont TV station KBMT. One of the nation’s largest oil refineries, the Exxon Mobil facility in Beaumont, wasclosed because of the storm, and Houston’s Bush International Airport was largely inaccessible. Jeff Lindner, meteorologist with the Harris County Flood Control District, warned in a tweet around 10:30 am CDT: “LIFE THREATENING flash flooding over metro Houston. Do NOT travel…if stuck in high water abandon the vehicle immediately.”

Phenomenal rainfall totals had piled up Thursday morning even as the event was still under way. The town of Hamshire, Texas, about 10 miles southwest of Beaumont and 60 miles east of Houston, reported 25.75” in 12 hours and a storm total of 33.58” from Monday morning through 9 am CDT Thursday. Another report in the same general area showed an unconfirmed storm total of 40.75” on Thursday morning. A personal weather station in Beaumont, TX recorded a 3-day precipitation amount of 36.08” as of 1:30 pm EDT Thursday.

The flooding rains are affecting many of the same areas devastated by rains from Hurricane Harvey just two years ago. Harvey set an all-time U.S. storm total rainfall record from a tropical cyclone of 60.58” in Nederland, TX, about 10 miles southeast of Beaumont, with 60.54” at nearby Groves. The largest 12-hour rainfall in U.S. records was the 34.30” that fell in Smethport, Pennsylvania, on July 18, 1942. The 24-hour U.S. record is 49.69” at  Waipā Garden, Kauai, Hawaii, on April 14-15, 2018—followed closely by the 42” that fell in Alvin, just south of Houston, during Tropical Storm Claudette on July 25-26, 1979.

Figure 2. Multi-sensor estimates of 24-hour rainfall across southeast Texas from Tropical Depression Imelda through 7 am CDT Thursday, September 19, 2019. At specific points, 24-hour totals will be higher than shown in these gridded estimates, and multi-day storm totals for Imelda will be higher still. Image credit: NOAA/NWS/AHPS.

As Imelda drifts slowly into northern Texas, the persistent west-to-east rainband over southeast Texas is likely to weaken by Thursday afternoon and evening. Imelda is predicted to weaken and no longer be a tropical depression by Friday evening. High-resolution models such as the HRRR and 3-km NAM—which correctly anticipated on Wednesday the threat of massive rainfall Wednesday night between Houston and Port Arthur—do not show a repeat event on this scale in this area for Thursday night. However, localized thunderstorms with torrential rain may redevelop somewhere between Imelda’s center and the Texas coast, according to the NOAA/NWS Weather Prediction Center. “While the activity overnight should not be able to match what we are seeing this morning over far southeast TX, it still has the potential to bring a significant flash flood threat and worth monitoring,” said WPC. They predicted an additional 4 – 8″ of rain could fall over southeast Texas, and 3 – 5″ over southwest Louisiana.

See the frequently updated weather.com article for more on Imelda’s evolving impacts. In this weather.com feature, Jon Erdman compares and contrasts the epic rainfall produced by Imelda and Harvey.

Jerry becomes a hurricane

The Hurricane Hunters measured 75 mph surface winds in Jerry late Thursday morning, making the storm a low-end Category 1 hurricane. Jerry is the tenth named storm and fourth hurricane so far in 2019; we’ve also had two major hurricanes so far this year—Dorian (Cat 5) and Humberto (Cat 3). An average Atlantic hurricane season has 8 named storms, 4 hurricanes, and 1 major hurricane by September 24, so 2019 is a busier-than-average season thus far.

Tropical storm watches are up for portions of the , since the center of Jerry is expected to pass about 50 – 100 miles to the north of the islands on Friday night and Saturday morning. At 11 am EDT Thursday, tropical storm-force winds extended out 45 miles to the south of the center, but this wind field is expected to expand as Jerry intensifies. By Friday night and Saturday morning, tropical storm-force winds are predicted to extend out up to 80 miles to the southeast. This expansion of the wind field could bring tropical storm conditions to several of the Leeward islands then, particularly and Anegada.

Figure 3. Hurricane Jerry at 12:20 pm EDT September 19, 2019. At the time, Jerry had just been upgraded to a Category 1 storm with 75 mph winds. Image credit: NOAA/RAMMB.

Track forecast for Jerry

Jerry was headed west-northwest at 16 mph at 11 am Thursday, and this motion is expected to continue for the next few days, with a turn to the north towards Bermuda this weekend. On this track, Jerry could be a threat to Bermuda on Tuesday. While the Thursday morning operational runs of the GFS, European, and UKMET models all agreed on this scenario, about 20% of the 50+ members of the 0Z Thursday run of the European model predicted that if Jerry underwent a strengthening trend that is not projected in other model runs or predicted by , the hurricane would feel a stronger influence from upper-level northeast winds that would take it more to the west, allowing it to miss recurvature and enter the Gulf of Mexico.

Disturbance south of and the Dominican Republic is worth watching

A tropical wave centered about 200 miles south of the Dominican Republic/Haiti border early Thursday afternoon was spreading heavy thunderstorm to eastern portions of the Dominican Republic. Satellite loops on Thursday afternoon showed that the disturbance had developed an elongated surface circulation that did not appear to be growing more organized, though heavy thunderstorm activity was increasing along its east side.

Wind shear was high, near 20 – 25 knots, due to strong upper-level winds out of the southwest. This shear was keeping the disturbance’s heavy thunderstorm confined to the east side. The disturbance was headed to the west-northwest to northwest at about 5 into an area of higher wind shear, making significant development unlikely, but this disturbance is still worth keeping an eye on. The disturbance will likely bring heavy rains to Haiti and the Dominican Republic Thursday and Friday, and to eastern Cuba Friday and Saturday. In their 2 pm EDT Thursday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 10%.

Tropical wave approaching Windward Islands may develop early next week

A tropical wave located midway between the coast of Africa and the Lesser Antilles early Thursday afternoon was headed west at about 15 mph. This disturbance, which had not yet been given an “Invest” designation by NHC, will likely spread heavy thunderstorms to Barbados on Saturday night and into the Windward Islands on Sunday. The tropical wave had support for development early next week from about 50% of the 21 members of the 0Z Thursday GFS model ensemble forecast, but none of the 50+ members of the 0Z Thursday European model ensemble. In their 2 pm EDT Thursday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 10% and 30%, respectively.

New African tropical wave may develop early next week

A tropical wave expected to emerge from the coast of Africa on Saturday has support for development early next week by about 50% of the 70+ members of the 0Z Thursday GFS and European model ensemble forecasts—as well as the 12Z Thursday operational run of the GFS model. This system is expected to move west then west-northwest later next week, following a path similar to the one Hurricane Jerry has taken. In their 2 pm EDT Thursday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 0% and 40%, respectively.

Jeff Masters co-wrote this post.

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