Eric Berger

Hurricane Hanna will make for a wet weekend in Houston

Good morning. As of 7am CT, the National Hurricane Center has just upgraded Hanna to hurricane status, with sustained winds of 75 mph. The storm should make landfall near or just north of Port Mansfield later today, and may strengthen further before doing so.

Storm surge projections for Hurricane Hanna. (National Hurricane Center)

For the greater Houston area, this ultimately will probably yield little change to our overall forecast for a rainy and breezy weekend. We are going to see elevated tides along the coast of 1 to 3 feet from Freeport to Galveston, and along other coastal areas. In addition, these regions near the water will see some stronger winds, with gusts likely above 30 mph, while inland areas see gusts of 25 mph or above.

Houston radar at 7:24am CT on Saturday. (RadarScope)

In terms of rainfall, we’re still expecting a wet weekend, with 2 to 4 inches of rainfall coming down across most of the area as Hanna’s outer rain bands traverse the area. Generally, these bands should be spread out, and keep moving—helping to limit accumulations. Some streets may briefly flood due to high rainfall rates, however. We can’t rule out some isolated accumulations of 6 or more inches over the southern part of the Houston region.

Healthy rain chances will continue through Monday or Tuesday before we finally return to somewhat more normal weather for summer, which is to say highs in the low 90s and scattered afternoon showers.

Hanna, Gonzalo, and a third tropical system. (National Hurricane Center)

After Hanna moves off, the tropics should remain active. While Gonzalo is expected to die in the southern Caribbean Sea there is another system behind it that will be spinning westward across the Atlantic Ocean toward the Caribbean. Most of the global guidance is bullish on this system eventually becoming a hurricane (it would be named Isaias), and it will probably be something for the islands, and eventually the United States to track. But it will be several days before we have any sense of where the storm may ultimately go.

In Houston, we are lowering our expectations for the Gulf depression

Houston has about two more months to go, in terms of prime time, for the 2020 Atlantic Hurricane Season. As long time readers of this site will know, the odds of Texas being hit by a hurricane after September 24th, are quite low. By all appearances, the next two months in the tropics will be quite busy, with the Atlantic’s Main Development Region already starting to heat up. So we are going to have plenty of systems to monitor. To survive this period of anxiety, therefore, we should prioritize which tropical systems are worth worrying about.

And we’re here to tell you, Houston, Tropical Depression Eight does not have the look of something we think the greater Houston area should worry too much about. The usual disclaimers apply, of course. This is the tropics. Things change. But at this point we’re trending toward moderate to minimal effects.

(Space City Weather)

To that end we’re lowering the entire metro area to a Stage 1 flood alert on our flood scale, bringing the coastal areas (previously Stage 2) into alignment with the rest of the area. Generally, we think most of the Houston area will see 1 to 4 inches of rainfall this weekend. The coast may see some blips above 5 inches, but over the course of a couple of days this should be manageable.

The biggest area of concern, in terms of rainfall, now appears to be an area from Matagorda Bay south to Corpus Christi, or Port Mansfield. We think there may be some bullseyes of 10+ inches in these areas. The depression, which may be on the verge of becoming Tropical Storm Hanna, is simply moving westward fast enough that it will hopefully limit long periods of heavy rainfall. We anticipate a landfall on Saturday morning, somewhere between Corpus Christi and Brownsville. Most of the strongest winds will be to the north of the landfalling location.

The 12z European model shows a landfalling storm at around sunrise on Saturday. (Weather Bell)

We will of course continue to track this depression, and if our forecast thinking changes we will update post haste. For now, however, you can expect a gray and wet weekend, but likely one without widespread street flooding, or worse.

Tropical Depression likely to make landfall Saturday in Texas

Good morning. This post will focus on Tropical Depression 8, because after today it will strongly influence our region’s weather through the weekend. Overall, our forecast for this tropical system has not changed a whole lot from yesterday: We are predicting a Stage 2 flood event for coastal counties (plus southeastern Harris County), and a Stage 1 event for inland areas of the Houston region. In short, for most, this probably will be a wet weekend, but not a wholly disruptive one. But as always with tropical weather we’re going to watch this one closely.

Space City Weather flood scale.

Thursday

After several wet days, with parts of the area such as Clear Lake and Pasadena picking up 5 to 7 inches of rainfall, today should bring partly sunny skies and some time to dry out swampy yards. Rain chances are probably below 20 percent for most, with warm afternoon sunshine helping to dry soils out and pushing highs into the mid-90s. This will be hottest day until at least early next week. Winds will be light, out of the east to northeast.

Friday

The forecast for Friday morning is similar, with low chances of rain through at least the morning hours and perhaps into the afternoon as well. However, starting around sunrise or shortly thereafter, we’re likely to see winds pick up out of the east to northeast at about 15 mph. Rain chances pick up during the evening and overnight hours as the outer bands of the tropical system reach our area. After that, our weather is largely dependent upon the tropical system’s track and the vagaries of its structure.

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We are forecasting a Stage 2 flood for the impending tropical system

This afternoon we’re issuing our first “flood scale” forecast for the Gulf disturbance, which is increasingly likely to move into Texas this weekend as a tropical depression or weak tropical storm. We are calling for a “Stage 2” flood event for coastal counties in the greater Houston area—Brazoria, Galveston, and Chambers as well as southeastern Harris County (i.e. the Clear Lake area). For inland areas we think this will be a Stage 1 event. As with all tropical weather, of course, this forecast is subject to change. (Read more about the scale, and why we created it).

Space City Weather flood scale.

Now let’s explain how we came to this forecast.

Satellite appearance

Let’s begin with the system itself, which at present is about due south of the border between Alabama and Mississippi, and moving nearly due west. The storm’s organization has improved today, adding westerly winds, which is a precursor to developing an overall circulation. Trends favor additional organization and we probably will see this named a depression or Tropical Storm Hanna later today or on Thursday. We expected this, but do not anticipate further strengthening to, say, a hurricane. Theoretically this is possible, but does not seem likely given the storm’s interaction with dry air, among other factors.

Gulf disturbance satellite presentation on Tuesday afternoon. (NOAA)

Track

The storm increasingly seems likely to move toward the central or southern Texas coast. The preponderance of ensemble members of the European and GFS models predict such a track. Certainly, without a well established center of low pressure it is important to not give too much credence to these predictions. But as we are perhaps just two or three days away from a Texas landfall, and there is good consistency in the track forecast, our confidence level in the track is moderate.

12z European model forecast tracks for the Gulf disturbance. (Weathernerds)

Rainfall

Unfortunately, knowing the track of a tropical system does not confer meteorological superpowers when it comes to trying to forecast rainfall totals. We believe the heaviest rains will be to the north of the storm’s center, but the “where” is difficult to say.

Some of the forecasting models we commonly use are starting to predict rainfall “bullseyes” of 10 inches for hardest hit areas, particularly along the coast. (This seems pretty reasonable for a tropical system like this). However, we do not have confidence in whether these highest totals will come in Corpus Christi, Galveston, or Port Arthur. It is because of this potential for 10 inches of rain in the Houston area that we are issuing a Stage 2 warning for coastal areas. We still think much of the greater Houston region will see 2 to 4 inches of rain over a couple of days, which is totally manageable.

European model ensemble forecast for average precipitation from the Gulf system. (Weather Bell)

Beyond this system

The National Hurricane Center may upgrade Tropical Storm Gonzalo to hurricane status tomorrow as it approaches the southern Caribbean Sea. Right now we have relatively low concerns about Gonzalo becoming a threat to the Gulf of Mexico. We will of course continue to watch it, but advise you to not lose any sleep over it. Beyond Gonzalo the tropics are going to remain active.