Posted by Eric Berger at 6:50 AM
Every year I struggle with whether to write this post—because there’s always a chance it will be wrong. However, the fact is after this date the chance of a hurricane striking Texas is vanishingly low, about 1-in-50 for any given year. I’ll discuss this more below, after the forecast.
Monday through Wednesday
Houston’s late summer-like pattern will persist over the area for the next few days, with hot days and highs of around 90 degrees, steamy nights in the 70s, and scattered showers. A few thunderstorms could be pretty strong, but most of Houston will see moderate, little, or no rainfall over the next three days. Area-wide accumulations will probably be measured in tenths of an inch, if that.
Thursday and Friday
Warmer weather will hang around as a cold front backs into the area from the northeast. These northeasterly winds should arrive by sometime on Friday, but we may not feel the drier or moderately cooler air until Friday night or Saturday morning. Until then we can expect more warm days and muggy nights, with slight rain chances.
Dewpoints early on Saturday morning show drier air “backdooring” into Houston. (Weather Bell)
Saturday and Sunday
Houston is going to have a great weekend to end September and begin October. It’s not going to be cold by any stretch, but the air will be drier and that will make a big difference. Expect mostly sunny skies with highs most likely in the mid-80s. Overnight temperatures should fall to the mid-60s for inland areas, with warmer conditions near the coast.
Posted by Eric Berger at 9:49 AM
Welcome to the weekend! Some rain chances will return to Houston later on Sunday, and most days next week. But it’s nothing we’re concerned about. In response to a number of questions about the tropics, however, we wanted to provide an update on all of the activity out there. We have a lot of it in the Atlantic.
As we get deeper into September, the Atlantic tropics remain active. (NOAA/Space City Weather)
This storm, which has been waggling around the tropical Atlantic for days, finally is beginning to follow a track—and this track may eventually lead to some tropical effects for the East coast. Here’s a look at the European model ensemble forecast for the center of Jose on Wednesday morning, which shows a fairly large tropical storm or hurricane moving up the east coast, but offshore, early next week.
European model Hurricane Jose position forecast for Wednesday morning. (Weather Bell)
Most of the model guidance suggests the storm will turn northeast by around Tuesday or Wednesday, and this would keep the center away from Long Island and Boston, Mass. Right now for those locations I’d expect some gusty conditions and swells, but nothing too significant. Some areas of Boston and Cape Cod could see 2 to 4 inches of rain, but again, nothing too extreme.
If the track for Jose moves west and brings the center to shore, and the storm becomes stronger than forecast, its effects could become more concerning.
Posted by Matt Lanza at 10:00 AM
During Hurricane Harvey, I think we did a good job making pretty clear that our focus was to be on flooding. And ultimately, the majority of the damage and devastation wrought by Harvey as it moved through our region came via water. But one of the most surprising and occasionally unsettling aspects about Harvey’s impacts on Southeast Texas were the tornadoes. The warnings came fast, they came furious, and a number of them were confirmed.
The fine folks over at U.S. Tornadoes put together a really nice summary of this event, which likely ranks Harvey close to or in the top ten for most prolific tornado-producing tropical systems in the United States.
The Houston National Weather Service forecast office issued over 150 warnings for tornadoes through the storm. During that hellacious Saturday night and Sunday morning, over 30 tornado warnings were issued, most of them overlapping with flash flood warnings. We strongly encouraged people to keep their phone alerts on that night because the frequency of tornadoes was almost shocking (and because of numerous videos of an actual tornado in northwest Harris County late that Saturday afternoon that sort of drove home the point). That, coupled with the flooding likely lead to a long, sleepless night for many in the area. I’ll have some comments about the phone alerting issue at the end of the post.
The early tornadoes
First, let’s recap some of the tornadoes that actually occurred. The NWS Houston office has confirmed nearly 30 tornadoes as of September 14th, all of them either EF-0 or EF-1 strength. Here’s a look at some of the tornadoes.
Posted by Eric Berger at 7:37 AM
When it comes to measuring the intensity of hurricanes, the most widely understood metric is sustained wind speed, and this morning Irma has regained some strength, to 130 mph. However for scientists, the more accurate determinant of intensity is central pressure—the extent to which a storm’s center is lower than the Earth’s normal sea-level pressure of 1013.25 millibars. This morning, Irma’s central pressure has been hovering just below 930 millibars. Although far from a record, only six US hurricanes have made landfall with pressures below this—The Indianola storm, the 1919 Florida Keys hurricane, the 1935 Labor Day storm, Camille, Andrew, and Katrina. All are legendary storms. This provides some sense of what is now crossing the Florida keys and moving toward the Florida peninsula.
Intensity and Track
Irma finally turned to the north-northwest on Saturday night. While the delayed turn was a surprise to some, we have been discussing the possibility of Cuba-then-southeastern Gulf of Mexico scenario since last Tuesday. The Cuba interaction weakened Irma substantially, from 160mph down to 120mph, but since moving back into the Florida Straits on Saturday afternoon, the storm has begun to regain some strength, to 130mph as of 7am CT Sunday.
Irma will now move through much higher wind shear than it has seen for days. (CIMSS/Space City Weather)
Fortunately, the window for restrengthening is short. Later today Irma’s center will begin to interact with the southwestern part of Florida, and this will disrupt the storm’s organization. Another critical factor is wind shear, the varying direction of wind speeds at different levels of the atmosphere. Irma has had a very smooth go of it for days (less than 20 knots). But it has now reached an area of higher shear (shown above), and this should help to weaken the storm considerably over the next day. Here’s the official forecast for winds over the next three days as Irma moves inland.
Forecast maximum sustained winds for Irma. (National Hurricane Center/Space City Weather)