Major Flood Threat This Weekend

Nearly two-thirds of the state of Texas along with almost the lower half of Louisiana could see some astonishing rainfall this weekend. The green-shaded areas depicted above are under flash flood watches. 

It is possible that over a foot of rain could fall, bringing dangerous conditions to locations that have been very dry for weeks. Remnants of record-setting hurricane Patricia will combine with a cold front progressing across the central Plains, setting the stage for widespread misery.

When I first saw the blaring headlines that the Pacific hurricane named Patricia was the "strongest on record", I thought it was more media hyperbole. However, this time, it's fact. The two main measures of hurricane potency are maximum winds and central pressure. The lower the pressure, the stronger the storm. Here's what it looked like. when it made landfall Friday evening:

This is different than impact, because a storm could strengthen over warm water, far from harming anyone. However, when that danger looms, it certainly gets our attention.

Here's an idea of how strong Patricia is compared to its predecessors:

STORM         YEAR        MAX WINDS  (mph)       CENTRAL PRESSURE (mb)
Patricia        2015               200                              879
Wilma          2005               185                              882
Gilbert        1988                185                              888
Labor Day    1935                185                             892
Rita             2005                180                             895
Allen           1980                190                             899

The storm will weaken with regard to those two parameters as it encounters the mountains of central Mexico, but the moisture from the storm will be drawn into southern and central Texas by Saturday. Here's what computer models show for Saturday afternoon:

By late Sunday, here's the projection for accumulated rainfall. The purple shading indicates amounts that could easily exceed one foot:

Residents in the watch areas should stay alert to rapidly changing conditions as rain will fall repeatedly over the same areas, leading to the flash flood threat. Remember the live-saving adage - turn around, don't drown. The majority of the fatalities from the catastrophic South Carolina flooding earlier this month occurred in cars. People either got trapped in rapidly rising water or they ignored "road closed" signs and drove around barricades.

Much-needed Rain Later This Week

As of this writing, 147 counties in Texas are under a burn ban due to dry conditions. Much-needed rain is in the forecast for later week as low pressure develops in the western Gulf. That, in combination with a strong high pressure cell in the southeast U.S. will allow for extensive periods of rain to move into some of the driest areas in the Lone Star State.

Already, a few spotty showers have developed off the upper Texas coast, a sign that the lower atmosphere is much more saturated than recent days. By Friday, the picture changes dramatically to this:

The low pressure develops by late Sunday and could linger in the Gulf for a while:

Once the rain begins late Thursday, it could deposit over half a foot in the Hill Country, which could lead to flood concerns:

The pattern will be periods of repeated rains over some of the same areas. In situations like this, dry soil actually increases the flood threat because runoff is stifled. 

The best thing to do is to monitor weather conditions and if you know you are in a flood-prone area, you should have a plan to get to higher ground. Continue to monitor this blog for updates heading toward the weekend.

 

Cool Fall Weekend Ahead!

Believe it or not, a cool front slipped through Southeast Texas late Friday night. The only way you'd know is because of a wind shift as there wasn't any rain and just a few high clouds. You'll definitely feel the difference as drier and cooler air descends down to the coast. Shown above are the forecast low temperatures by Sunday morning.

High pressure filling in behind the front dominates the weather for much of the up-coming week. Gradually, by the end of next week, the high will slide off to the east. Then, a return of southeast winds pushes temperatures higher, increases the humidity and eventually brings rain back to the region.

For the past few days, the long-range GFS model has been hinting that low pressure will develop in the Gulf. Where it ends up and how intense it becomes is still a bit uncertain. However, there is a good chance that widespread, heavy rain will spread from Corpus Christi through Houston and into East Texas. Here's a depiction for the last Sunday of the month:

This will need to be monitored to see exactly where the low forms and more importantly, how much rain falls and where. Until then, enjoy the crisp mornings and warm afternoons!

 

Joaquin's Journey

The third hurricane of the 2015 has become the strongest. Today, Joaquin was found to be packing 130 mph winds, making it a dangerous category 4 hurricane. Very warm water and weak upper-level steering conditions are creating the perfect environment for growth. Residents in the southern Bahamas are reporting widespread flooding and wind damage Thursday afternoon. So the question now is, where will Joaquin head next? Here's the latest forecast from the National Hurricane Center:

It still shows the storm remaining just off shore and not making landfall. For the past few days, models that forecast movement have been waffling between sending the storm out to sea and taking aim at some point of the east coast. Not surprisingly, the official track from the National Hurricane Center has been quite wide, nearly paralleling the east coast. This is intended to demonstrate the uncertainty of the forecast.

There are two major complicating factors steering this storm. The first is a stalled cold front, which is draped along the east coast. This has brought some heavy flooding rains from parts of Maine down to South Carolina:

At the same time, there is an upper-level low pressure cell in the southeast that may draw Joaquin northward over the weekend as well as enhance moist conditions from the mid-Atlantic to the southeast:

Computer projections have varied because the location and strength of the upper-low in the Southeast is uncertain. It seems that each day's computer model runs makes a different determination of where the upper-level low will end up.

This afternoon, the so-called spaghetti model plots have a split decision, with roughly half of them trending toward a mid-Atlantic landfall by Sunday and the other half sending the storm toward Bermuda:

There is virtually no chance of Joaquin heading into the Gulf of Mexico, so this will largely be an East Coast concern. It is also interesting to note that in the last 10 years, there have been fourteen Category Four hurricanes, most of them occurring in late September or October. Most have impacted the Caribbean or meandered in the middle of the Atlantic. The last Category Four hurricane to hit the U.S. was Charley in 2004.

Continue to watch for my blog updates on this dangerous storm to see where it ends up. If you know folks along the East Coast, encourage them to remain watchful and to be prepared. Even if the hurricane doesn't make a landfall, the stalled out front could bring more heavy rain that may lead to flooding.

Showers Make A Comeback

Keep the umbrella handy Tuesday as a weak disturbance in the Gulf sends showers toward the upper-Texas coast. The last few days featuring warm, but not overly humid weather, and pleasant mornings is about to change.

High pressure in the Southeast U.S. will allow for southeast winds to develop, which always means a return of muggy weather to Houston. Additionally, there are signs of low pressure in the western Gulf of Mexico.

Typically, a low in the Gulf might raise a few eyebrows, even though we've reached the peak of hurricane season. However, the low is very weak and very disorganized. Also, there isn't high pressure aloft. The latter would make tropical development a bit more favorable.

Expect showers today to develop as those southeast winds send Gulf showers inland. The afternoon could be especially soggy and even in the morning, there may be considerable cloudiness. 

Once Tuesday's rain threat diminishes, the rest of the week looks rain free, although the southeast winds will make the days warm and muggy and the mornings not quite as pleasant as they have been recently. Lows should range in the mid to upper 60s.

Change On The Horizon

No sign of summer's end today as the heat beat wears on across the Lone Star. Nothing really unusual about that after Labor Day. However, there are signs of change later in the week. It is very likely that a cold front, currently dragging through the middle of the country is headed toward Texas.

Along the front, showers and in some cases, stronger thunderstorms are likely to develop. The front should make it through Dallas by Wednesday and then arrives along the Upper Texas coast by Thursday. Here is a projection for rain and the front then:

The slow-moving nature of this front means rain chances could linger well into the weekend. It's still a little early for THE cold front that puts and end to the seemingly endless summer, but it will be a welcome sign.

Soggy Start To September

Even though rainfall in August was .66" below normal, there were only five days with rain in Houston. So the forecast for wet weather over the next few days is a good thing. The image above shows the water vapor imagery for Texas. The bright white indicates moisture, the red area indicates dry sections. 

An upper-level disturbance near Corpus drifts slowly northward, spreading rain chances upward and inward today and tomorrow. With little steering it, showers could linger through late in the week. Here are projections for Tuesday and Wednesday:

There are no concerns as of yet for flash flooding as there should be decent breaks between rainfall episodes. Best advice: keep the rain gear handy.