Radar indicates that Harvey’s center is passing through Matagorda on its way back out into the Gulf of Mexico. Maximum sustained winds are 40 mph, so Harvey is barely hanging on as a minimal tropical storm. Most of the tropical storm force wind is out over the water, although Bush Intercontinental Airport reported a wind gust to 46 mph this afternoon. The storm is meandering in a generally east-southeast direction at only 3 mph, and is expected to continue this motion until shifting to the northeast midweek.
One question everybody is asking is if Harvey will strengthen again since at least part of the storm (including the center) will be back over the warm Gulf waters. While there could be some slight strengthening, we don’t expect Harvey to become a hurricane again. In fact, it might not even become a strong tropical storm. One reason can be seen on this water vapor satellite image from the new GOES-16 satellite (with thanks to the College of DuPage website). See the orange color wrapping across the southern part of the storm? That’s dry air aloft, a big negative for intensification of any tropical system.
But remember: this is just a reference to wind. Even a weak or former tropical system…remember Allison?...can dump incredible amounts of rain. As I’ve discussed through the weekend, as long as we remain on Harvey’s eastern and northern flank, heavy rain bands will continue to plague parts of our metropolitan area. The National Weather Service released seventy-two hour rain totals earlier this afternoon, and a number of reporting stations are now well over thirty inches of total rainfall. You can see those totals here...
Unbelievably, not only is more rain on the way, but a LOT of rain in some areas. Take a look at the latest raw data from our in-house high resolution RPM model…these are projected rain totals from midday Monday through Wednesday morning.
As you can see, areas roughly from Houston eastward stand the best chance to receive another sixteen-to-twenty inches of rain. That means that, by the end of the storm, some localized rainfall amounts between forty-five and fifty inches are possible. The only adjective that I haven’t seen used yet to describe what’s happening to us right now is “Biblical.”
So when will this all finally end? As you can see from our very latest RPM model run, Harvey will meander across southeast Texas through the day Tuesday. Many models don’t nudge Harvey far enough northeast to end the rain until Thursday, but there is some disagreement about the endgame, as can be expected when the models are dealing with weak steering currents.
As for the flooding itself, that’s even more difficult to predict an end to. Remember that our area is made up of what are called watersheds. As these incredible rainfall amounts fall on our watersheds, the water has to flow somewhere, and that is naturally dictated by two things: gravity and terrain (obviously, there are also human elements that impact flooding…such as water release from reservoirs…but I won’t deal with those). The gravity part is simple: water flows from higher to lower elevations. The terrain part is also simple: there is greater flooding and runoff in urban areas than rural areas due to there being more concrete surface in the urban areas. So the question that remains is how fast the water will travel downstream in the watershed. The reason I wanted to explain this is that higher flood levels will occur in some areas after the rain ends this week, so don’t let your guard down as we approach the precipitation end of one of our nation’s most historic weather events.
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