heavy rainfall Archives - Reduce Flooding

TS Sara Rainfall Totals Meeting, Exceeding Hurricane Harvey’s

11/17/2024 – According to a National Hurricane Center report at 6 AM this morning, slow-moving Tropical Storm Sara has produced around 40 inches of rain in northern Honduras. To put that amount in perspective, it meets or exceeds most Hurricane Harvey totals reported in Harris County during a similar 4-day period.

Harvey 4-Day Totals

Rainfall can vary widely over areas. Harris County Flood Control District’s (HCFCD) final report on Hurricane Harvey shows total Harvey rainfall amounts ranged from 26 to 47 inches across the county during a 4-day period. The lowest totals occurred over the northwest and northeast part of the county with the highest totals focused across the southeast part.

Clear Creek at I-45 saw the maximum 47.4 inches.
San Jacinto at US59 saw 32.7 inches.
Spring Creek at I-45 saw 29.4 inches.
Cypress Creek at Cypresswood Drive saw 34.9 inches
Luce Bayou at FM2100 saw 31.8 inches.

Most places in Harris County reported 4-day totals in the 30-40 inch range. Some were slightly lower, some slightly higher. Clear Creek was the statistical outlier.

Harvey in Historical Perspective

Hurricane Harvey struck the Gulf Coast in August 2017. It was one of the most significant and devastating tropical storms in U.S. history, primarily due to the sheer volume of rainfall it produced.

Harvey’s rainfall ranked among the heaviest ever recorded in the continental United States from a tropical system. The highest peak occurred in Nederland, about 85 miles east of Lake Houston. It still holds the official U.S. record for a single-location rainfall from a tropical storm – 60.58 inches.

Harvey’s rainfall was not only extreme in terms of totals but also in how long the rain persisted. The storm’s slow-moving nature allowed the moisture to be dumped over the same areas for four days, contributing to catastrophic flooding, especially in Houston.

Update on TS Sara

Four days also matches the amount of time Sara has dumped rain over northern Honduras.

Tropical Storm Sara — *Location and size of TS Sara at 7 AM CST*

Sara’s heavy rains are now spreading westward across portions of Belize, Guatemala, and the Yucatan Peninsula.

Sara should hold steady in strength with tropical-storm-force winds of around 40 MPH until it moves inland later today. NHC warns that it will likely cause “significant and life-threatening flash flooding and mudslides” across Belize, El Salvador, eastern Guatemala, western Nicaragua, and the Mexican State of Quintana Roo.

Sara is no threat to Houston, but could cause heavy rainfall in Florida later this week after it crosses into the Gulf as a tropical depression.

In mountainous regions, such as northern Honduras, the volume of rain is not the only danger. So is the speed of the runoff as we saw earlier this year when Helene hit North Carolina.

Posted by Bob Rehak on 11/17/24

2637 Days since Hurricane Harvey

Heavy Rainfall, Hail, High Winds, Tornados, Street Flooding Possible Today

The National Weather Service (NWS) Storm Prediction Center and Harris County have issued outlooks for today that include risks of heavy rainfall, hail, high winds, tornadoes and street flooding.

NWS predicts an “enhanced risk” of severe weather (3 on a scale of 5) with a 10%-14% chance of tornados. NWS rates the excessive, heavy rainfall risk as slight (at least 15%).

Light rainfall has already begun in the Lake Houston area and will increase throughout the morning hours as storms approach and pass through. The threat should be past us by 3-4 PM, just in time for school pickup.

*NWS severe weather outlook as of 12:01 a.m. CST.*

*NWS tornado outlook as of 12:01 a.m. CST.*

*NWS excessive rainfall outlook as of* 1:55 a.m. Houston time.

Rainfall Accumulation

Jeff Lindner, Harris County’s meteorologist, warns, “Forecasters have tended to increase rainfall amounts over the last 24 hours with the potential for storm clustering and cell training in southwest to northeast bands.”

Lindner says rainfall amounts of 1-3 inches appear to be common today with higher isolated totals of 4-5 inches especially for areas south of I-10, where activity may linger into the evening hours.

Moisture levels will be high for late November. Plus onshore winds will feed more moisture into the area. Widespread showers and thunderstorms are likely.

Some models show banding and training of storms this afternoon into the evening hours. But that’s for areas mainly south of I-10 and around Galveston Bay (SE Harris, Liberty, Chambers, Galveston, Brazoria Counties).

Potential for 1-2 Inches Per Hour, Street Flooding

Soils are generally dry over the area, but hourly rainfall rates of 1-2 inches per hour may result in some street flooding at the usual flood-prone locations.

The front will sag off the coast tonight into early Friday, but you can expect additional disturbances across the region on Friday with showers and thunderstorms expanding inland toward the I-10 corridor.

Wind and Hail

While much focus has been on the tornado threat, we also have the potential for damaging wind and large hail. Stronger showers may produce 40-50mph winds today. Additionally, gradient winds of 25-30mph with a few higher gusts will be common over the area for much of the day with the coastal locations seeing the stronger winds.

Posted by Bob Rehak on 11/30/23 at 7:40 a.m. based on information from NWS and Jeff Lindner

2284 Days since Hurricane Harvey

Potential For More Heavy Rainfall Continues into Midday

According to Harris County Meteorologist Jeff Lindner, we can expect more heavy rainfall today. Showers and thunderstorms have developed this morning with a line of thunderstorms extending from near Columbus to near Bay City. Showers and thunderstorms are also developing ahead of this line.

Lindner also adds that the storms’ forward motion is fast enough to help limit any one area from experiencing an excessive amount of rainfall.

More concentrated showers and thunderstorms will likely move into Houston metro area between 6 and 8 a.m. This may result in some street flooding under the heaviest storms. Activity will linger into the midday hours.

Primary Heavy Rainfall Threat During Morning Hours

As the low pressure system over central Texas begins to lift northward today, drier air will move in from the west and rainfall will become increasingly isolated during the afternoon hours.

Additional rainfall this morning of 1-2 inches will be common with isolated totals of 3-5 inches under any areas of cell training.
Jeff Lindner, Harris County Meteorologist

Main threat remains street flooding through the morning hours. While rises on area creeks and bayous will be likely with heavy rainfall this morning, the chances for significant and widespread flooding are low.

Beyond Today

The unsettled weather pattern will continue into late week. This weekend and early next week, another slow moving upper level system over northern Mexico will slowly progress into Texas.

Those storms will probably drop more rain on central and southwest Texas than southeast Texas. But how and whether they advance eastward is still in question.

The more significant flood threat this weekend will focus west of Houston. However, showers and thunderstorms will be possible in the Houston area through the weekend and into next week.

Forecasted Rainfall Today

*Source: National Weather Service’s Weather Prediction Center* *5/10/23*

Forecasted Rainfall Next 7 Days

Posted by Bob Rehak on 5/10/2023 based on info from Harris County

2080 Days since Hurricane Harvey

Heavy Rainfall Threat Approaching

Last week, I posted about the possibility of heavy rain early this week. Last night, Dallas experienced torrential rains and they’re headed this way. One amateur weather gage on Londonderry Lane reported more than 14″ of rain! Dallas/Fort Worth officially received 9.46 inches of rainfall in 6 hours and 7.8 inches in 3-hours. Significant flash flooding has resulted. A 1-hour storm total of 3.01 inches was recorded at DFW with a storm total of 6.54 inches. That wiped out 67% of the area’s 2022 rainfall deficit in a few hours.

*National Weather Service map as of 12:41 pm Houston time. Purple boxes represent flash flood warnings. Bright green = Flood warnings. Dark green = flood watch.*

Threat Will Increase From North to South During Next 24 Hours

According to Jeff Lindner, Harris County Meteorologist, the frontal boundary over north Texas will slowly move southward today and approach the northern portions of southeast Texas by mid- to late afternoon. Numerous showers and thunderstorms will develop along the boundary along with scattered showers developing northward along the seabreeze and Gulf inflow.

The air mass will become extremely moist and unstable. When combined with slow moving/stalled boundaries, excessive rainfall can result. Lindner says areas north of HWY 105 have the first potential for heavy rainfall in early afternoon. Then the front will slowly sink southward toward I-10 tonight into early Tuesday. Expect slow storm motions, cell training, and back-building of cells to the west and northwest. Everything points to heavy rainfall.

While grounds are dry, the local air mass will be capable of some impressive short duration rainfall amounts of 2-4 inches in an hour.
Jeff Lindner, Harris County Meteorologist

This was clearly seen overnight in north Texas. The local air mass will not be much different over southeast Texas. Especially N of I-10. These rainfall rates can lead to rapid flash flooding especially in urban areas.

Widespread rainfall amounts of 2-4 inches are expected over much of southeast Texas through mid week. But Lindner also expects isolated higher totals of 6+ inches. And where these higher totals occur, flash flooding will be possible, he says.

Confidence in rainfall is high. But confidence in rainfall amounts and location of the heaviest rainfall is low.

Street flooding will be the primary threat with the heavy rainfall rates. Rises on area creeks and bayous will be possible if some of the heavier storms train or move slowly over any watershed.

Overall, this wet pattern will linger into late week. But a slightly drier air mass will eventually push through and we should transition back toward a more “normal” cycle of showers and thunderstorms driven mostly by the seabreeze front.

See the National Weather Services predictions below.

Posted by Bob Rehak on 8/22/22 based on information from HCFCD and NWS

1819 Days since Hurricane Harvey

Two More Rounds of Heavy Rain Yet to Come; Flash Flood Watch Extended Through Sunday

Heavy rainfall remains possible through Sunday.

Flash Flood Watch remains in effect until Sunday morning for much of the area.

Widespread heavy rainfall along and north of I-10 over the last 24 hours has resulted in rainfall amounts of 2-3 inches over much of that area. Pockets have received 4-5 inches. Those include northern Waller and western Montgomery Counties. Portions of Walker County received 4-6 inches.

*Last 24 hours of rainfall as shown on Harris County Flood Warning System at 7pm 4.30.21.*

Ongoing flooding through much of today closed several roads in low lying areas of northern Waller and Walker Counties. Run-off continues to progress down creeks and into mainstem rivers. Rises will continue along upper Spring Creek into tonight and Saturday. However, at the moment forecasters expect no significant flooding. See attached graphics for 24-hr rainfall totals and current channel status.

First Round Kicks Off Overnight

NWS satellite imagery shows moisture streaming up out of Mexico as of 7PM Friday. The area along the middle Texas coast from the coastal bend up to to about Wharton looks favorable for the formation of another round of heavy to excessive rainfall late tonight and early tomorrow. Models indicate this activity will occur mostly west of I-45 and south of I-10 into Saturday morning before it begins to weaken. Exactly how far northeast rain and heavy rain may spread is still in question. But according to Jeff Lindner, Harris County’s meteorologist, “The latest thinking indicates it will remain southwest of the areas hard hit today.”

Second Round of Storms Saturday Night into Sunday

Lindner predicts a weakening of the storm Saturday afternoon. But he warns to expect numerous showers and thunderstorms Saturday evening. He says they will invade the region from the southwest to northeast. Moisture levels will support heavy to excessive rainfall rates within any organized thunderstorms.

Rainfall Amounts

Expect additional rainfall amounts of 1-3 inches over the weekend with isolated totals reaching 4-6 inches…especially around the coastal bend and Matagorda Bay tonight into early Saturday.

Area Soils Now Saturated

I received 3.07 inches in my rain gage today and have standing water in my yard. Soils have become nearly saturated in areas that saw the greatest rainfall today, while areas around Galveston Bay have experienced little rainfall thus far. Heavy run-off in many areas north of I-10 will cause rises in several channels. Keep an eye on the East Fork of the San Jacinto River at FM 1485 into the weekend. The forecast there currently exceeds flood stage.

A good amount of water is routing into the West Fork of the San Jacinto also. But current forecasts keep the river from Conroe to Humble below flood stage. The SJRA is releasing water from Lake Conroe at almost 6000 cubic feet per second. Despite that, the lake level has risen almost a foot and a half today above its normal pool level.

The areas north of the lake received some of the highest rainfall totals this morning. This lake is now 3.5 feet above where it was when the SJRA stopped the seasonal lowering last week. Had they now lowered the lake a foot, it would be even higher now. We can all learn from this experience.

Minor flooding will also be possible this evening along upper Spring Creek west of Hegar Rd with rural low lands near the creek inundated.

Additional rainfall over the weekend may change some of the current forecasts.

Posted by Bob Rehak on 4/30/21 at 8PM based on info from the NWS and Harris County Meteorologist Jeff Lindner

1340 Days since Hurricane Harvey

Heavy Rainfall Potential Tonight, Through Weekend

UPDATED AS OF 10PM THURSDAY – Jeff Lindner, Harris County’s meteorologist, warns that heavy rainfall potential will spread across the region tonight through the weekend.

*Rainfall accumulations expected by NWS in **next 5 days**. Updated at 5:51PM Houston time on 4/29/2021.*

National Weather Service has issued a Flash Flood Watch for much of Southeast Texas tonight through Sunday morning. However, the risk is slight.

*Most of the Houston region has a marginal or slight risk of flash flooding – less than 20%.*

Lakes Houston, Conroe Being Lowered

Houston Public Works is currently lowering Lake Houston by 12 inches, from 42.5 feet to 41.5 feet in response to the newly updated forecast – 3 inches of rain in our watershed within 24 hours. Property owners along the lake should secure property along the shoreline. To monitor current water levels at Lake Houston, visit www.coastalwaterauthority.org.

The SJRA had stopped its seasonal release from Lake Conroe. Rains from last weekend pushed the lake back up past its normal full pool level of 201 feet. As of 7pm Thursday, the SJRA had not resumed releasing any water, but by 10pm it had.

*Lake Conroe level as of 7pm on 4/29/2021*

*As of 10pm, SJRA had started releasing 530 cubic feet per second.*

To monitor SJRA releases, see the dashboard on their home page.

Inflow from Gulf Will Collide With Stalled Front over SE TX

“A slow-moving, upper-level, low-pressure system over the southwest will combine with a surface front that will move into southeast Texas later today,” says Lindner. He expects the fronts to stall over our area. He says they will produce numerous rounds of showers and thunderstorms from late this afternoon into Sunday.

Onshore flow has increased moisture over the region with dewpoints running in the low to mid 70’s. The surface front extends from northeast Texas to near Laredo. It will move slowly into southeast Texas late this afternoon and then likely stall between downtown and the coast by Friday morning. Other disturbances, says Lindner, will ride along this frontal boundary toward the northeast helping to produce several rounds of showers and thunderstorms.

With the upper level winds becoming increasing parallel to the stalling surface front and moisture levels remaining high into the weekend, the threat for heavy rainfall will be increasing. Storm motions are expected to slow on Friday, but coverage remains scattered, so some areas could see some decent rainfall while other get little.

Threat Remains Through Sunday

Expect widespread storms to develop on Saturday morning as the threat for cell training increases.

The slow moving upper level low will then move directly across the area on Saturday night into Sunday with additional rounds of thunderstorms…some of these storms could be severe along with more heavy rainfall.

Widespread rainfall amounts of 1-3 inches will be possible with isolated totals of 4-5 inches. With all the moisture in place, high rainfall rates could cause street flooding.
Jeff Lindner, Harris County Meteorologist

Lindner warns potentially higher totals are possible given the overall slow moving nature of the weather pattern.

Increasing Runoff as Grounds Saturate, Marginal Risk of Flash Flooding

The dry ground conditions now in place means soil will absorb much of this rainfall. Regardless, Lindner predicts rises on area creeks and bayous. He says that grounds will begin to saturate over the weekend yielding greater run-off as the storm wears on.

The National Weather Service has all of southeast Texas in a marginal risk for flash flooding starting Friday and into Saturday.

Posted by Bob Rehak on 4/29/2021 based on information by Harris County Meteorologist Jeff Lindner and the National Weather Service

1339 Days since Hurricane Harvey

Heavy Rainfall, Strong Thunderstorms Likely Friday, Saturday

A series of strong storm systems will converge over south Texas late this week bringing heavy rainfall. Moisture will rapidly increase Thursday afternoon and evening.

Black Friday Looking Like Bleak Friday

“We may even see development of showers over the coastal waters Thursday afternoon that begins to spread inland Thursday evening,” says Jeff Lindner, Harris County’s meteorologist. “Expect showers and thunderstorms to increase and expand in coverage and intensity early Friday. A warm front may begin to slow or even stall over southeast Texas from Friday afternoon into early Saturday. That will allow prolonged heavy rainfall due to cell training.”

Moisture profiles for the Friday afternoon into Saturday point toward heavy rainfall.

“Ingredients are in play for prolonged heavy rainfall, cell training, and possible flash flooding.”
Jeff Lindner, Harris County Meteorologist

Then a cold front will approach the region at some point Saturday into early Sunday helping to focus additional rainfall. The upper level trough will slowly move eastward late Saturday into Sunday leading to decreasing rain chances and cold conditions.

Up to 5-6 inches Rainfall Possible with Hail Threat

A few of the storms on Friday and Saturday could be strong with the main threat being small hail.

Rainfall amounts over the next 5 days (mainly Friday and Saturday) will likely average 1-3 inches over the region with isolated totals of 5-6 inches possible.

Grounds are dry, so much of this rainfall will likely be beneficial. It will help mitigate increasing drought and fire-weather concerns.
Jeff Lindner

Marginal Risk of Flash Flooding

“However,” says Lindner, “should any sort of heavy rainfall axis develop and anchor over any specific location for a period of time…flash flooding could develop. The main concern would be street flooding with the heavier rainfall rates, but rises on area creeks and bayous will be possible in heavy rainfall materializes in the more urban areas.”

*Five day rainfall forecast* *shows 3-4 inches in the Houston Area.*

*NOAA gives Houston a marginal chance of flash flooding this weekend.*

Posted by Bob Rehak on 11/25/2020

1184 Days since Hurricane Harvey

Potential for Heavy Rainfall, Flash Flooding Increasing This Week

Low-pressure System Will Meander Near Coast

Lake Charles and Houston radars show numerous clusters and bands of heavy rainfall across Gulf waters associated with deep tropical moisture. These bands will soon begin to move onshore.

*Lake Charles radar shows numerous bands of heavy showers just offshore headed this way.*

*Houston Hobby radar shows similar banding.*

Cumulative Rainfall Potential Through Friday

*Excessive Rainfall Outlook on Wednesday this Week.*

According to Jeff Lindner, Harris County meteorologist, the National Weather Service and National Hurricane Center, models have come into agreement. They predict a surface-low pressure system may form just offshore on Tuesday and drift inland over southeast Texas Tuesday night into Wednesday. The National Hurricane Center currently gives the system only a 10% chance of tropical formation…

…BUT regardless heavy rainfall should result.

Ingredients appear to be coming together late Tuesday through Thursday for a heavy rainfall event over the region.

Endless Supply of Tropical Moisture

According to Jeff Lindner, Harris County meteorologist, “An endless supply of moisture will pump into the region. Formation of slow-moving, training rain bands appears likely over portions of the area.”

This weather system could produce excessive rainfall, enough to saturate dry ground in a short period of time. Rains today and Tuesday especially south of I-10 will saturate dry ground. Conditions by Wednesday should support much more run-off, over a wider area.

10-15 Inches Possible

Widespread rainfall amounts of 3-6 inches will be likely over much of the area with isolated totals of 10-15 inches possible.

Hourly rainfall rates of 3-4 inches will be possible under any training bands and any slow-moving clusters resulting in rapid-onset urban flash flooding. The threat for creek, bayou, and river flooding will increase by mid-week as grounds become increasingly saturated and run-off increases.

Flash flooding will be possible.

Posted by Bob Rehak on 9/16/2019 as of 9 a.m.

748 Days since Hurricane Harvey

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