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Friday, May 29, 2015

Just Can't Get A Break

The Norman Number in Houston for Friday, May 29 is 6. Morning downpours head into the Gulf. A few more spotty showers may develop in the muggy air, otherwise partly cloudy and warm. High: 85.

Still reeling and recovering from the extensive flooding earlier in the week, Southeast Texas braces for yet more rain. Thanks to swollen rivers and bayous, additional rains will cause new rises and new flood fears.

A steady-moving line of storms emerged from North Texas late Thursday night, prompting a renewed Flash Flood Watch. Fortunately, that threat diminished around daybreak as the storms weakened considerably despite ominous skies.

That short-lived respite from another threat of heavy downpours won't last, however. A muggy airmass over the region will allow for a few isolated showers, mainly along the coast Friday. 

By Saturday, a cold front will begin moving southward from the Red River valley. It has the potential for widespread rain. Here's a model depiction for Saturday afternoon:

Not out of the question - more training storms that could lead to flash flooding. Rainfall amounts could fall in the 1" to 2" range. 

There is a glimmer of hope toward the beginning of next week. as a weak ridge of high pressure forms in the Northern Gulf. This could potentially suppress heavy rainfall, but even a few spotty showers could linger.

Looks like this month will go down as one of the wettest Mays ever in Houston. As of today, the 13.59" is the fifth highest total. With two days left in the month, only 2.28" would have to fall to best the 15.87"mark set in 1907. Given how things have been going, that wouldn't be too surprising.

Tuesday, May 26, 2015

Historic Flooding!

                                           (I-45 at North Main - courtesy +AlexGreen713

Overnight deluges turned interstates into waterways, stranding thousands. Bayous and rivers overflowed their banks and continue to rise. The map above shows the astonishing totals across Harris county. If you didn't know better, you might think a tropical system came through as the totals climb to nearly a foot. Much of that fell in five hours.

Hardest hit, parts of southwest Houston. Alief picked up over 9", Sugar Land over 10". Both official airport locations set daily records with Bush at 4.34" and Hobby at 3.95". For the month, this May is the 10th wettest. Even as residents struggle to recover, more wet weather is on the way later this week.

A vigorous upper-air disturbance collided with a steadily-moving bow echo last night. But there was an extra ingredient that came into play. An odd westward-moving boundary from Louisiana created extra lift. All of those systems have since moved east and potentially, rain-weary Houstonians could get a break Tuesday and Wednesday. However, a new disturbance is slated to move across Texas by Thursday and Friday that could cause more rain. 

Check back here Friday for an update on that and the chances May 2015 could move up in the record books.

Friday, May 22, 2015

Time For An Ark?

The #NormanNumber™ in Houston for Friday May 22 is 5. Scattered showers drift across town under mostly cloudy skies with a muggy feel. High: 81°

Heading into the unofficial start of summer this Memorial Day weekend, don't expect to see much sun. It's rained 13 out of the 21 days so far this month, many of them drenching downpours. Wish there was better news, but more soggy days are in the forecast.

Historically, May is one of the wetter months in Houston averaging 5.09" - this year's total is nearly 6". As much as that is, we'd have to have almost twice as much to come anywhere near record territory.  A familiar pattern sets up this weekend as southeast winds sweep Gulf moisture inland. Here are the expected totals over the next three days:

While parts of Southeast Texas could see anywhere from 2" - 4", up to 8" is possible form north-central Texas into central Oklahoma. 

Looking beyond the weekend, there could yet be more soggy days during the last full week of May. As we hope to dry out, remember that when this month ends, hurricane season starts. Hopefully, we can avoid more excessive rain that usually accompanies "those" tropical threats, especially early in the season.

Tuesday, May 19, 2015

A Break Coming Soon?

Tired of days of rain? Well, there could be a day this week where little falls from the sky. The above depicts the total rainfall which fell Monday; much of it north and northwest of downtown Houston and the Galveston Bay region. Radar estimates colored in red and purple suggests over 6 inches accumulated leading to brief flash flooding.

A series of slow-moving upper-level disturbances has been the cause of the nearly week-long deluges prompting flood watches and warnings. There are still quite a few watersheds that need to monitored including the San Jacinto and Trinity rivers.

Showers are in the forecast again Tuesday, as yet another disturbance moves through. However, once that one passes, a bubble of high pressure could protect the region for at least a day. That could bring a return of bona fide sunshine which could help dry things out a little. Here's a computer projection for the weather map Wednesday:

By Thursday and Friday, the wet pattern reestablishes itself, so the reprieve will be short-lived. One thing is for sure, there could be a bumper crop of skeeters to content with in the weeks to come.

Wednesday, May 13, 2015

Deluges Not Done

The last 24 hours have seen torrential rains turn streets into rivers and forcing bayous and rivers out of their banks around the Houston area. The bad news - there is more wet weather on the way. A flash flood watch remains in effect until 7 pm CDT. See the current rainfall amounts here. The hardest hit areas have been around Clear Lake and League City.

Why is this happening? Two factors come together as they often do: a stalled coastal front and a series of upper-level disturbances. The same front responsible for the destructive plains tornadoes that developed during Mother's Day weekend stalled out along the upper-Texas coast late Monday. A series of low pressure waves moving out of the Hill Country create the lift allowing storms to develop. Those storms develop along similar paths, leading to the "training" effect that causes too much rain repeatedly.

Several more disturbances are coming through today and here is a projection for how much more rain could fall across Texas;

While the majority of the rain could fall from Dallas to San Antonio, any more rain across Southeast Texas could inflame still-swollen rivers and bayous. Brace for more wet days through the end of the week with a possible break by the weekend.

Friday, May 8, 2015

Hello Ana!

The first named tropical system of the year was declared late Thursday night off the South Carolina coast. Hurricane hunter planes identified maximum winds of 45 mph, well above the 39 mph threshold used to give such closed circulations a name.

The system is called sub-tropical due in part to the cool air aloft, as opposed to a tropical system which has a warm core above it. The system is also "cut off" from the main jet stream steering winds so it's in no hurry to go anywhere. That will mean a windy and squally weekend anywhere from Charleston to North Carolina's outer banks. A tropical storm watch is in effect from Edisto Beach South Carolina to Cape Lookout North Carolina.

Here's the official forecast from the National Hurricane Center, indicating Ana could come inland late Sunday night:

The familiar "cone of uncertainty" highlighted in light blue indicates the  possible variability of the track of Ana and the likely extend of the higher winds. Don't focus on the black line; it merely indicates where the center of the storm will travel. The impacts could be anywhere within the blue envelope. Additionally, Ana will cause increased swells, high waves and some minor coastal flooding as waters could rise anywhere from 1 to 2 feet.

The circulation is also fairly tight and is not expected to strengthen too much beyond its current values and isn't likely to become a hurricane.

Read more about the connection between early-forming storms and the rest of the season.

Wednesday, May 6, 2015

Duck and Dodge The Rain

Keep the umbrella handy today and for the next few days as periodic bouts of rain are expected across Southeast Texas. The above depicts widely scattered showers and thunderstorms developing during the afternoon today.

As is often the case, the key is the word "widely". Many may not see much rain at all, while others could experience brief, heavy downpour. Southeast winds bring an abundant flow of moist air in from the Gulf. Today's rains will be triggered by weak upper-air disturbance. Once it passes, the rest of the week's rains will happen sporadically in the humid air.

Bottom line: keep the umbrella handy in case you are caught in one of those brief downpours.

Saturday, May 2, 2015

And Now A Word From The Tropics

First, let me say that no one along the Texas coast needs to be concerned about an imminent threat from the Gulf of Mexico. There's plenty of time to dissect any and every wave poised to possibly take aim at any part of the U.S. Remember, Hurricane Season doesn't even begin for another month. However in the forecast snapshot above, a wave developing over the Caribbean may, just must may become a sub-tropical low off the South Carolina coast by Wednesday.

This system should remain off the coast for several days as a wedge of high pressure stretching from the Ohio River Valley to the Gulf Coast remains fairly stout. It is this same high pressure that brought the Southeast a delightful first weekend of May. Nevertheless, if it gets as organized as is forecast, the National Hurricane Center may declare this the first named storm of 2015 - Ana. 

Above is the forecast for Thursday, which shows a much-stronger system, that could lash the South Carolina coast with +50 mph winds and possibly high swells. It is a situation that will be monitored through the up-coming week.

The system will be unlike a traditional tropical system in that it will have a cool upper-level core instead of a warm one. However, it's intensification may be due to something tropical systems over 
water have - it will be over warm water. In this case, the warm swath of water called the Gulf Stream that emerges from the Gulf of Mexico and slides parallel to the Eat Coast of the U.S.