More than half a foot of rain is set to fall in the nation’s fourth-largest city during the next few days from this system as it approaches Houston from the Gulf of Mexico, sending multiple rounds of heavy thunderstorms slowly lumbering ashore. The National Weather Service cautions that some locations could see a foot or more of rain before this event ends Thursday, raising flash flood concerns. Rainfall rates in the heaviest bands could approach 3 inches per hour.

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At the same time, Category 2 Hurricane Humberto is on its way to major hurricane status as it churns toward a position just north of Bermuda late in the week. A tropical storm warning is up for the island, as the storm is forecast to remain far enough away to spare it from its worst winds and heaviest rains.

Meanwhile, an additional disturbance over the open tropical Atlantic has become a tropical depression and is forecast to become a tropical storm and then a hurricane in the coming days as it meanders west-northwestward. Assuming it reaches tropical storm-strength, it will be named Jerry. Computer models expect this storm to pass near or just north of the Lesser Antilles, but it’s not yet clear where it will go from there.

Dangerous flood threat unfolding in Texas

The rain was already pouring down in buckets on the Texas Gulf Coast on Tuesday morning, where flash flood watches blanketed the greater Houston metro area.

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Shower and thunderstorm activity will continue to blossom Tuesday from the Matagorda coast to Port Beaumont, with a couple bands of rainfall spreading into southwestern Louisiana. The flood risk in Louisiana, particularly from Sabine Lake through Lake Charles, is increasing as well.

A widespread 5 to 10 inches, with localized higher amounts, may fall through Wednesday afternoon in the Houston-Galveston corridor.

A tropical storm warning was posted for Sargent to Port Bolivar along Texas’ coast, and includes Galveston.

“The difference of just a few miles could be the difference of several inches of rain,” the NWS wrote, stressing the highly variable nature of thunderstorm-driven rainfall totals. While 1- to 3-inch per hour rainfall rates are possible, they’ll be realized only beneath the heaviest downpours. But where these downpours do repeatedly traverse the same areas, dangerous flash flooding and top-tier rainfall totals may result.

It’s not out of the question that one or two very isolated locales pick up a foot and a half of rainfall.

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By Thursday, uncertainty in the forecast increases. It will probably still be raining in Houston. But will the storm interact with some approaching energy aloft and shift the axis of heaviest rainfall farther east? That would be good news for the Interstate 45 corridor, but bad news for coastal Louisiana. While still not the most likely solution right now, the odds for that scenario have increased some since Monday. However, there’s an equal or greater shot that the rains continue Thursday in the Houston area, as the area of low pressure over the Gulf strengthens some as it moves inland.

This latest episode underscores the fact that storms do not need to be a hurricane to be dangerous. Most recently, Hurricane Harvey painted a dire picture of what just water can do, with a record 60.58 inches on Nederland, Tex. With a price tag of $125 billion, it ties with Katrina as the costliest U.S. tropical cyclone on record. And most of the damage occurred when it was a tropical storm.

This time, Imelda could rank among the heaviest rainfall producers on record in some Houston suburbs. Have a plan to take action should a flash flood warning be issued for your location.

Humberto to become major hurricane and sideswipe Bermuda

A tropical storm warning is up for Bermuda, where Humberto could make a close pass later this week.

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As of Tuesday morning, the Category 2 storm was about halfway between the United States and Bermuda. According to the National Hurricane Center, “Humberto is expected to become a major hurricane by [Tuesday night] or Wednesday morning.” Humberto’s cloud shield is nicking the coastal Carolinas, which are contending with rough surf and rip currents, but otherwise its impacts are largely relegated to the open ocean.

On the forecast track, Humberto is predicted to track well north of Bermuda on Wednesday night into Thursday, clipping the British island territory of 65,000 with its outermost rain bands. Tropical storm-force winds of greater than 39 mph are possible, along with rip currents and 1 to 3 inches of rain.

Tropical depression forms east of the Lesser Antilles

The National Hurricane Center announced a new tropical depression formed Tuesday morning about midway between the Leeward Islands and Cape Verde. Forecasters at NHC say it’s likely to become a tropical storm by Tuesday evening.

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The incipient storm is on a track westwards, though a curve to the west-northwestward is anticipated as it intensifies. It may become a hurricane by late Thursday or Friday, with a track taking it ominously close to Puerto Rico and perhaps the southeastern Bahamas.

The track is uncertain at this point. However, models have been inching it closer to land masses, with the “out to sea” scenario a little bit less likely now. However, modeling weak tropical systems can be especially challenging until clearly defined circulation centers become better established, which should happen by Tuesday night.

This is a storm that needs to be closely watched in the days ahead.

A sudden uptick?

It’s possible that there will be a potentially significant uptick in Atlantic tropical storm and hurricane activity during the last week in September and extending through early October. The anticipated awakening of the tropical Atlantic is thanks to a overlap of weather systems that will encourage rising air over the Atlantic’s main development region, to the west of Africa and east of the Lesser Antilles.