As of 10:00 a.m. Monday morning, the National Hurricane Center (NHC) still shows the center of Tropical Storm Beta located offshore. The latest forecasts from the NHC predict that Beta will move onshore near Matagorda Bay, then move up the coastline toward League City.
The NHC also advises that the storm has picked up speed. Yesterday, they estimated 3 mph; today 7 mph.
No one seems to predict that the storm will intensify before landfall.
“Dry air continues to work into and wrap around the large wind field of Beta yielding the disorganized precipitation field with the system.”
Lake Houston Area is the blue dot in the center of the swirl. Red line is predicted path of Beta.Source: Weather Live.
Main Threat: Storm Surge
At this time, Beta’s main threat is to the coastline through storm surge. “Tides are currently running 4.0-4.5 feet in Clear Lake and across coastal sections of Harris County with several sites near the Gulf beaches running 4.0-4.5 feet. Coastal flooding is ongoing and will continue for much of the day. Several roadways are underwater along the coast and around Galveston Bay,” says Lindner.
Lindner continues, “As Beta makes landfall along the middle Texas coast later today, the storm will begin to slow and then turn ENE toward the upper TX coast. It will slowly weaken along the way. This track will keep onshore flow along the upper Texas coast tonight and Tuesday. Tides will remain high into the high tide tonight. Impacts along the coast will continue through the day and into tonight and likely Tuesday.”
Wind Forecast
The most likely arrival time of tropical storm force winds, if we get them, is later tonight.
Tropical storm force winds already cover a large part of the mid-Texas coast.
The storm will weaken as it moves toward the Houston Area and turn into a tropical depression. The further north you live from the coastline, the less intense winds will be.
Depending on where you live in Houston, you have a 30% to 100% chance of experiencing topical storm force winds. The Lake Houston Area is on the low end of that range. The National Weather Service predicts that the Lake Houston Area has a chance of seeing 39-57 mph winds. But Spaces City Weather advises that Beta is “not a significant wind threat.”
However, note that tropical-storm-force winds currently extend outward up to 175 miles (280 km) from the center of the storm.
Galveston has reported sustained winds of 39 mph and a gust of 43 mph during the past couple of hours.
Rainfall
Dry air has worked into the circulation of Beta, according to Lindner. “This has resulted in a more disorganized and scattered rainfall pattern. However, the system is still capable of heavy rainfall especially near the center later today and in bending structures east of the center for the next 48 hours.”
Models show several banding features developing during the next 48 hours over SE TX, But little consensus exists on where the heaviest rainfall totals may be.
Lindner advises that, “Given that much of the area will reside on the eastern side of a the tropical system, we should keep some level of concern of heavy rainfall and flooding in place through the next 48 hours.”
Lindner predicts that widespread rainfall amounts of 4-8 inches will be possible for areas along and south of I-10 with isolated totals of 10-12 inches under any training feeder bands. Totals to the north of I-10 will likely average 3-5 inches with isolated totals of 6-7 inches.
However, the NHC predicts slightly less rain. See the map below.
As long as the rainfall spreads out over the next 48 hours, most of the creeks and bayous can handle the expected rainfall amounts, Lindner says. But should any training develop, flash flooding would be possible.
Watches and Warnings in Effect
A Storm Surge Warning is in effect for Port Aransas, Texas to Rockefeller Wildlife Refuge, Louisiana. That includes Copano Bay, Aransas Bay, San Antonio Bay, Matagorda Bay, Galveston Bay, Sabine Lake, and Lake Calcasieu.
A Tropical Storm Warning is in effect for Port Aransas Texas to Morgan City Louisiana. That includes the Lake Houston Area.
A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA WITHIN 36 HOURS.
Lindner, the NHC and NWS all warn that tornadoes remain a threat with this storm. Especially, tonight and Tuesday.
Track
Yesterday, models predicted that Beta would track up US59 toward the Humble/Kingwood Area. However, today, forecasters think the storm will track closer to the coast. They put it on a line toward League City.
Wind shear will keep Beta’s track close to the coastline, but it will also affect the cyclone’s intensity along with land interaction. The closer the cyclone stays near the Gulf of Mexico, the more likely that bands of convection containing tropical-storm-force winds will continue to roll onshore the Texas coast through 36-48 hours.
Summary
Flash, urban, and isolated minor river flooding is possible, but the danger is “slight.”
Net: Beta is still a threat. But it may be less of one than yesterday. That’s because of the dry air folding into the system and wind sheer which seem to be weakening it somewhat. Be hopeful, but cautious. Expect several inches of rain and high winds in the next two days with both tapering off Wednesday.
Posted by Bob Rehak on 9/21/2020 at noon based on data from NHC, NWS, Jeff Lindner, Space City Weather and Weather Live
1119 Days after Hurricane Harvey and 368 since Imelda
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/09/Screenshot-2020-09-21-at-11.37.19-AM-scaled.jpg?fit=1183%2C2560&ssl=125601183adminadmin2020-09-21 11:46:032020-09-21 11:52:04Beta Moving Ashore Today Then Likely Tracking Slightly South of Houston
As of mid-day Sunday, all of East Texas now faces some level of excessive rainfall and flash flood risk from Tropical Storm Beta.
The projected path of the storm has shifted inland, so rainfall will reach father north. The latest track now takes the storm on a path right up US59 from Sugar Land to Humble and Kingwood. However, Beta likely be a tropical depression by the time it reaches the north side.
Harris, Montgomery and Liberty Counties (and the whole Houston region) face a high to moderate threat of flooding rains. The first rainbands from Beta have already started to move onshore today, but the heaviest rain will not occur until Monday into Tuesday.
North Houston Under Moderate Flooding Rain Threat
Flash Flood Watch in Effect
The entire region is under a flash flood watch. Coastal areas also face storm surge and tropical storm warnings.
Slow Moving Storm Will Produce Prolonged Rains
Beta is meandering slowly at about 3 mph northwest toward the coastline west of Houston and will then curl back over Houston. It should move inland sometime Monday or Monday night and turn from a storm into a depression by the time it reaches Houston.
However, Beta could dump rain on us from later today all the way through Wednesday.
40-50% Chance of Tropical Storm Force Winds Reaching North Houston
The North Houston Area has a 40-50% chance of seeing tropical storm force winds from Beta.
If the high winds reach this far inland, they would likely arrive Monday evening. Winds extend outward from the center for 195 miles as of Sunday morning.
Feeder Bands Extend Outward 190 Miles
In fact, at 11 a.m. Sunday morning, the first feeder band was approaching the eastern side of Houston, as you can see in the radar image below.
This image shows how the wind and rain from Beta could remain with us for days as the storm’s center wanders around the Gulf.
These feeder bands reach out 190 miles. That is roughly the distance from Houston to San Antonio. So Beta will produce long-duration rainfall from the middle Texas coast to southern Louisiana.
Flash, Urban, and River Flooding Likely
The National Weather Service warns that coastal flooding will remain a threat through midweek with the worst of the storm surge anticipated on Monday and Tuesday.
Elsewhere impacts from the excessive rain include:
Rainfall flooding may prompt evacuations and rescues.
Rivers and tributaries may rapidly overflow their banks.
Small streams, creeks, canals, and ditches may become dangerous rivers.
Flood control systems and barriers may become stressed.
Flood waters may cover escape routes.
Streets and parking lots may become rivers of moving water with underpasses submerged.
Driving conditions may become dangerous.
Many roads and bridges may close with some weakened or washed out.
Lake-Level Situation
According to the SJRA, Beta has the potential to dump up to 8 inches of rain in Montgomery County.
SJRA is operating under standard protocols for a severe weather event and will be onsite at Lake Conroe throughout the duration of Tropical Storm Beta.
Lake Conroe remains 18 inches low, and based on the current forecast, no reservoir releases are expected.
You can monitor stream and river levels in near-real time at Harris County Flood Warning System. Make sure you check out the inundation mapping feature.
Posted by Bob Rehak on 9/20/2020 based on information from the National Weather Service and National Hurricane Center
1118 Days after Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/09/HGXFloodingRainThreat.png?fit=492%2C745&ssl=1745492adminadmin2020-09-20 12:53:402020-09-20 13:32:59Excessive Rainfall Threat from Beta Spreads Inland
As Tropical Storm Beta bears down on the Houston Area, many people in the Elm Grove/North Kingwood Forest area worry that they might flood again. How likely is that, given the current predictions of 6-10 inches? After all, on May 7 last year, Elm Grove flooded on what was officially a six inch rain according to the nearest gage at West Lake Houston Parkway and the West Fork.
…But Detention Based on Pre-Atlas 14 Rainfall Rates
Even though that’s far more than Woodridge Village had during the May or September floods, the detention calculations by LJA Engineering were based on pre-Atlas 14 rainfall rates. A 100-year rainfall then was about 40% less than the official 100-year rainfall now.
So, the questions is, “How much rain would Beta have to dump on Woodridge Village before it overwhelmed the detention ponds that exist today?”
Figures Used by LJA
The chart below shows the rainfalls that the ponds were designed to hold without flooding. The bench mark its the 24-hour, hundred year rain.
These figures come from the hydrology report submitted by LJA to Montgomery County. A table buried on page 32 of the PDF shows that they based their analysis on a pre-Atlas 14, 100-year storm that dropped 12.17 inches of rain in 24 hours.
From Page 2.1 of LJA Hydrology Report Addendum, 8/28/2018 (page 32 of pdf.)
The ponds should also hold any of the shorter-duration rainfalls in the last column above.
Assumptions Underlying the Answer
To answer the question – How much would it take to flood Elm Grove again? – we need to make several assumptions:
LJA correctly calculated the volume needed.
Contractors actually excavated the volume promised.
With those caveats in mind, it would take 12+ inches of rain in 24 hours to exceed the capacity of the detention ponds currently on Woodridge Village. After that, water would start to overflow.
Short, High-Intensity Downpours Can Cause Different Type of Flooding
However, consider the other durations in the chart above. Seven inches in three hours or nine inches in six hours could also exceed the capacity.
Actually, as you get into these short-duration, high-intensity rainfalls, you introduce the risk of flooding from a second source: overwhelming the capacity of storm drains.
Storm Drains Designed for 2″ Per Hour
The storm drains in Kingwood are designed to convey about two inches of rain per hour. When you exceed that, water begins to back up in the streets. Exceed it enough, and water could actually enter homes – without sheet flow from Woodridge Village.
NHC Rainfall Prediction Spans 5 Days
The six-to-ten inch prediction issued by the National Hurricane Center for Beta spans five days. That’s good news. If ten inches were evenly spread out over five days, the streets, drains and ditches could easily handle two inches per day.
But those short, high intensity rainfalls – when you get two inches in five or ten minutes – represent a real danger. There’s just nowhere for the water to when it comes down that quickly.
Perhaps the Biggest Danger
Even if we got the predicted 6-10 inches all in one day, that’s still, at most, about 80% of the old 100-year rain which the detention was designed for.
I suspect the biggest danger from Beta may be those short, high-intensity cloud bursts or training feeder bands that dump a couple inches in five or ten minutes.
So keep your eye on the rain gage. Sign up for alerts at the Harris County Flood Warning System. Also, keep your eye on the forecasts; uncertainty still exists with Beta, its track and rainfall potential.
Posted by Bob Rehak on 9/19/2020
1117 Days after Hurricane Harvey and 1 year after Imelda
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/09/Rainfall-Table-Page-32-LJA-report.png?fit=730%2C350&ssl=1350730adminadmin2020-09-19 20:11:192020-09-19 20:21:44How Much Rain Would It Take To Flood Elm Grove Again?
Beta Moving Ashore Today Then Likely Tracking Slightly South of Houston
As of 10:00 a.m. Monday morning, the National Hurricane Center (NHC) still shows the center of Tropical Storm Beta located offshore. The latest forecasts from the NHC predict that Beta will move onshore near Matagorda Bay, then move up the coastline toward League City.
The NHC also advises that the storm has picked up speed. Yesterday, they estimated 3 mph; today 7 mph.
No one seems to predict that the storm will intensify before landfall.
Main Threat: Storm Surge
At this time, Beta’s main threat is to the coastline through storm surge. “Tides are currently running 4.0-4.5 feet in Clear Lake and across coastal sections of Harris County with several sites near the Gulf beaches running 4.0-4.5 feet. Coastal flooding is ongoing and will continue for much of the day. Several roadways are underwater along the coast and around Galveston Bay,” says Lindner.
Lindner continues, “As Beta makes landfall along the middle Texas coast later today, the storm will begin to slow and then turn ENE toward the upper TX coast. It will slowly weaken along the way. This track will keep onshore flow along the upper Texas coast tonight and Tuesday. Tides will remain high into the high tide tonight. Impacts along the coast will continue through the day and into tonight and likely Tuesday.”
Wind Forecast
The most likely arrival time of tropical storm force winds, if we get them, is later tonight.
Tropical storm force winds already cover a large part of the mid-Texas coast.
The storm will weaken as it moves toward the Houston Area and turn into a tropical depression. The further north you live from the coastline, the less intense winds will be.
Depending on where you live in Houston, you have a 30% to 100% chance of experiencing topical storm force winds. The Lake Houston Area is on the low end of that range. The National Weather Service predicts that the Lake Houston Area has a chance of seeing 39-57 mph winds. But Spaces City Weather advises that Beta is “not a significant wind threat.”
However, note that tropical-storm-force winds currently extend outward up to 175 miles (280 km) from the center of the storm.
Galveston has reported sustained winds of 39 mph and a gust of 43 mph during the past couple of hours.
Rainfall
Dry air has worked into the circulation of Beta, according to Lindner. “This has resulted in a more disorganized and scattered rainfall pattern. However, the system is still capable of heavy rainfall especially near the center later today and in bending structures east of the center for the next 48 hours.”
Models show several banding features developing during the next 48 hours over SE TX, But little consensus exists on where the heaviest rainfall totals may be.
Lindner advises that, “Given that much of the area will reside on the eastern side of a the tropical system, we should keep some level of concern of heavy rainfall and flooding in place through the next 48 hours.”
Lindner predicts that widespread rainfall amounts of 4-8 inches will be possible for areas along and south of I-10 with isolated totals of 10-12 inches under any training feeder bands. Totals to the north of I-10 will likely average 3-5 inches with isolated totals of 6-7 inches.
However, the NHC predicts slightly less rain. See the map below.
As long as the rainfall spreads out over the next 48 hours, most of the creeks and bayous can handle the expected rainfall amounts, Lindner says. But should any training develop, flash flooding would be possible.
Watches and Warnings in Effect
A Storm Surge Warning is in effect for Port Aransas, Texas to Rockefeller Wildlife Refuge, Louisiana. That includes Copano Bay, Aransas Bay, San Antonio Bay, Matagorda Bay, Galveston Bay, Sabine Lake, and Lake Calcasieu.
A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE EXPECTED SOMEWHERE WITHIN THE WARNING AREA WITHIN 36 HOURS.
Lindner, the NHC and NWS all warn that tornadoes remain a threat with this storm. Especially, tonight and Tuesday.
Track
Yesterday, models predicted that Beta would track up US59 toward the Humble/Kingwood Area. However, today, forecasters think the storm will track closer to the coast. They put it on a line toward League City.
Wind shear will keep Beta’s track close to the coastline, but it will also affect the cyclone’s intensity along with land interaction. The closer the cyclone stays near the Gulf of Mexico, the more likely that bands of convection containing tropical-storm-force winds will continue to roll onshore the Texas coast through 36-48 hours.
Summary
Net: Beta is still a threat. But it may be less of one than yesterday. That’s because of the dry air folding into the system and wind sheer which seem to be weakening it somewhat. Be hopeful, but cautious. Expect several inches of rain and high winds in the next two days with both tapering off Wednesday.
Posted by Bob Rehak on 9/21/2020 at noon based on data from NHC, NWS, Jeff Lindner, Space City Weather and Weather Live
1119 Days after Hurricane Harvey and 368 since Imelda
Excessive Rainfall Threat from Beta Spreads Inland
As of mid-day Sunday, all of East Texas now faces some level of excessive rainfall and flash flood risk from Tropical Storm Beta.
The projected path of the storm has shifted inland, so rainfall will reach father north. The latest track now takes the storm on a path right up US59 from Sugar Land to Humble and Kingwood. However, Beta likely be a tropical depression by the time it reaches the north side.
Six to 15 Inches of Rain Now Predicted
According to the local National Weather Service office and the National Hurricane Center, most of the Houston region can expect 6 to 15 inches with the highest totals closer to the coast.
Harris, Montgomery and Liberty Counties (and the whole Houston region) face a high to moderate threat of flooding rains. The first rainbands from Beta have already started to move onshore today, but the heaviest rain will not occur until Monday into Tuesday.
North Houston Under Moderate Flooding Rain Threat
Flash Flood Watch in Effect
The entire region is under a flash flood watch. Coastal areas also face storm surge and tropical storm warnings.
Slow Moving Storm Will Produce Prolonged Rains
Beta is meandering slowly at about 3 mph northwest toward the coastline west of Houston and will then curl back over Houston. It should move inland sometime Monday or Monday night and turn from a storm into a depression by the time it reaches Houston.
However, Beta could dump rain on us from later today all the way through Wednesday.
40-50% Chance of Tropical Storm Force Winds Reaching North Houston
The North Houston Area has a 40-50% chance of seeing tropical storm force winds from Beta.
If the high winds reach this far inland, they would likely arrive Monday evening. Winds extend outward from the center for 195 miles as of Sunday morning.
Feeder Bands Extend Outward 190 Miles
In fact, at 11 a.m. Sunday morning, the first feeder band was approaching the eastern side of Houston, as you can see in the radar image below.
This image shows how the wind and rain from Beta could remain with us for days as the storm’s center wanders around the Gulf.
These feeder bands reach out 190 miles. That is roughly the distance from Houston to San Antonio. So Beta will produce long-duration rainfall from the middle Texas coast to southern Louisiana.
Flash, Urban, and River Flooding Likely
The National Weather Service warns that coastal flooding will remain a threat through midweek with the worst of the storm surge anticipated on Monday and Tuesday.
Elsewhere impacts from the excessive rain include:
Lake-Level Situation
According to the SJRA, Beta has the potential to dump up to 8 inches of rain in Montgomery County.
SJRA is operating under standard protocols for a severe weather event and will be onsite at Lake Conroe throughout the duration of Tropical Storm Beta.
Real-time information on lake level can be found on the SJRA homepage at the “Lake Operations and Rainfall Dashboard” link.
At of this writing, Lake Houston is down a foot compared to its normal pool level (41.38 vs 42.4). You can monitor Lake Houston levels via the Coastal Water Authority website.
Monitor Downstream River Levels
You can monitor stream and river levels in near-real time at Harris County Flood Warning System. Make sure you check out the inundation mapping feature.
Posted by Bob Rehak on 9/20/2020 based on information from the National Weather Service and National Hurricane Center
1118 Days after Hurricane Harvey
How Much Rain Would It Take To Flood Elm Grove Again?
As Tropical Storm Beta bears down on the Houston Area, many people in the Elm Grove/North Kingwood Forest area worry that they might flood again. How likely is that, given the current predictions of 6-10 inches? After all, on May 7 last year, Elm Grove flooded on what was officially a six inch rain according to the nearest gage at West Lake Houston Parkway and the West Fork.
Additional Detention in Woodridge Village Now…
First of all, understand that upstream conditions have changed. On May 7th, only about 11% of the planned detention pond capacity had been constructed. And only 23% was constructed by Imelda. Today, 100% is in place.
…But Detention Based on Pre-Atlas 14 Rainfall Rates
Even though that’s far more than Woodridge Village had during the May or September floods, the detention calculations by LJA Engineering were based on pre-Atlas 14 rainfall rates. A 100-year rainfall then was about 40% less than the official 100-year rainfall now.
So, the questions is, “How much rain would Beta have to dump on Woodridge Village before it overwhelmed the detention ponds that exist today?”
Figures Used by LJA
The chart below shows the rainfalls that the ponds were designed to hold without flooding. The bench mark its the 24-hour, hundred year rain.
These figures come from the hydrology report submitted by LJA to Montgomery County. A table buried on page 32 of the PDF shows that they based their analysis on a pre-Atlas 14, 100-year storm that dropped 12.17 inches of rain in 24 hours.
The ponds should also hold any of the shorter-duration rainfalls in the last column above.
Assumptions Underlying the Answer
To answer the question – How much would it take to flood Elm Grove again? – we need to make several assumptions:
With those caveats in mind, it would take 12+ inches of rain in 24 hours to exceed the capacity of the detention ponds currently on Woodridge Village. After that, water would start to overflow.
Short, High-Intensity Downpours Can Cause Different Type of Flooding
However, consider the other durations in the chart above. Seven inches in three hours or nine inches in six hours could also exceed the capacity.
Actually, as you get into these short-duration, high-intensity rainfalls, you introduce the risk of flooding from a second source: overwhelming the capacity of storm drains.
Storm Drains Designed for 2″ Per Hour
The storm drains in Kingwood are designed to convey about two inches of rain per hour. When you exceed that, water begins to back up in the streets. Exceed it enough, and water could actually enter homes – without sheet flow from Woodridge Village.
NHC Rainfall Prediction Spans 5 Days
The six-to-ten inch prediction issued by the National Hurricane Center for Beta spans five days. That’s good news. If ten inches were evenly spread out over five days, the streets, drains and ditches could easily handle two inches per day.
But those short, high intensity rainfalls – when you get two inches in five or ten minutes – represent a real danger. There’s just nowhere for the water to when it comes down that quickly.
Perhaps the Biggest Danger
Even if we got the predicted 6-10 inches all in one day, that’s still, at most, about 80% of the old 100-year rain which the detention was designed for.
I suspect the biggest danger from Beta may be those short, high-intensity cloud bursts or training feeder bands that dump a couple inches in five or ten minutes.
So keep your eye on the rain gage. Sign up for alerts at the Harris County Flood Warning System. Also, keep your eye on the forecasts; uncertainty still exists with Beta, its track and rainfall potential.
Posted by Bob Rehak on 9/19/2020
1117 Days after Hurricane Harvey and 1 year after Imelda