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Potential tropical storm could douse northern South America and Aruba

A second tropical rainstorm could bring localized flooding to southeast Texas this weekend.

The cone of concern for what may soon become Bonnie. (NOAA/NHC) (NOAA/NHC/NHC)
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Three separate tropical weather systems are roaming the warm tropical Atlantic waters, circumstances more typical of the peak of the hurricane season, which is still about two months away. All have a chance to develop further, including one in the Gulf of Mexico that could deliver a drenching tropical rainstorm to coastal Texas and another swirling near Venezuela that could earn the name Bonnie.

Most of the attention is on Potential Tropical Cyclone 2, a lengthy title assigned to the conglomerate of thunderstorms and downpours north of coastal Venezuela and Colombia, where tropical storm warnings are in effect. It drenched the Windward Islands with heavy rainfall and is now cruising through the southern Caribbean. Tropical storm warnings are also up for Bonaire, Curaçao and Aruba. These locations are so far south that they rarely see tropical storm impacts.

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Behind it is another tropical wave with 30 percent odds of becoming a depression or a named storm. Regardless of how it evolves, additional heavy rain is slated for the Lesser Antilles.

There is concern growing closer to home, however, with a system in the northwestern Gulf of Mexico that has increasing odds of development. Flooding is possible in coastal Texas, including across the Houston-Galveston metro area, with some locales expected to receive half a foot of water or more.

Experts have long since been calling for an extra busy summer and fall hurricane season, marking the seventh consecutive anomalously active season. This season could easily lurch into active or even “hyperactive” territory, with around 20 named storms expected.

Soon-to-be-Bonnie

On Wednesday morning, the system that is expected to become Bonnie was unusually far south, skirting along at latitude 11.3 degrees North. That places it just a hair offshore of Venezuela, or 200 miles east-southeast of Curaçao. It was moving west at 30 mph.

Maximum sustained winds were at 40 mph, which is the threshold needed to classify it as a tropical storm. However, organization is a criterion, too. Until the system wraps itself around a cohesive central vortex, it won’t fit the bill of a tropical depression. And it won’t really be able to strengthen.

“If I just took a casual look at conventional satellite data, I would think the system was already a tropical storm,” wrote Eric Blake of the National Hurricane Center in an online technical forecast discussion. “There is a big ball of [downpours and thunderstorms] near the center … Microwave [satellite] data, however, does not show much low-level structure … and no obvious indications of a well-defined center. Thus, the system remains a disturbance.”

Irrespective of technicalities, tropical storm conditions have been realized thus far, including in Grenada, where Maurice Bishop International Airport gusted to 52 mph during the early morning hours.

The storm will pass near Aruba in the next 24 hours, bringing heavy rain, gusty winds and minor coastal splash-over. Since the year 2000, only four tropical systems have come within 60 miles of Aruba. The system has consistently trekked along at the southern edge of the envelope of computer model simulations.

That’s what makes for a tricky forecast. Interaction with land can shred tropical cyclones, disrupting their inner core or even spelling their demise. With this potential tropical storm, however, an inner core and center of circulation hasn’t formed yet. So long as the system brushes against the shoreline, it will remain scrambled, but a center may try to materialize to the north.

Where the system is going

Initially it looked like soon-to-be Bonnie would take a slightly more northern track and pass through the central Caribbean. That would allow it a bit more time to organize, and a marginal hurricane would have been possible into Friday or the weekend.

With the more southern track, however, odds are it will be slower to gather steam. It’s probably going to become a tropical storm late Wednesday or early Thursday. By then it will be swirling near or over the northern tip of Colombia before heading due west toward Nicaragua. It will impact there and northern Costa Rica late Friday or Saturday.

By that point, a higher-end tropical storm may be in the cards, along with excessive rainfall and possible mudslides in the higher terrain. A general 4 to 8 inches are likely, with a few spots topping 1 foot.

Thereafter, the Hurricane Center is forecasting the storm to continue chugging along into the eastern tropical Pacific, making the crossover and retaining enough organization to keep its name and maintain tropical storm strength. In fact, there are some signals that suggest the storm could persist into the second week of July assuming it survives its trip across the continental divide, buzzing through the open ocean before curving northward.

This potential tropical storm has saturated the atmosphere in its wake, making it easier for another tropical wave to plow west. It will arrive in the Leeward Islands and bring heavy rainfall by the weekend, but the Hurricane Center only estimates a 30 percent chance of development into a depression or tropical storm.

Tropical trouble in the Gulf

Meanwhile, there’s an increasingly robust clumping of showers and thunderstorms in the northwestern Gulf of Mexico. Thus far it’s outperformed forecasts, showing greater signs of organization than anticipated.

A broad but obvious low-level swirl is visible from the GOES-East weather satellite, but it’s exposed — meaning there aren’t thunderstorms over it. That’s ingredient number one: the presence of spin, and a concentrated low-level vortex and spiraling surface level flow. There are a few thunderstorms, including some tall, robust ones, but they’re divorced from the spin and are tethered northeast of the center.

The primary wild card at this point is whether one of the thunderstorms drifts over the low-level vortex and vertically stretches it. If that happens the storm could fill in quickly around it. That said, the window of opportunity is shrinking. It only has another day and a half at most over the water.

From there, moderate to heavy rain will overspread parts of Southeast Texas along the coastline, particularly from Houston-Galveston to Matagorda Bay. Friday into Saturday will be the wettest days, with some localized flooding possible. A widespread 3 to 6 inches is possible, with 8-inch amounts not unlikely.

It underscores that a storm doesn’t have to have a name to have an impact.

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