Tropical Storm Fiona

There's no absolute certainty in weather forecasting. But the future of Tropical Storm Fiona, the most recent in a trio of named storms, is more uncertain than the storm's two immediate predecessors, Danielle and Earl.

As of this evening, Tropical Storm Fiona had a sustained wind of 40 mph and was roughly 850 miles to the east of the Leeward Islands.

The official National Hurricane Center forecast is for the tropical storm to slowly strengthen but remain below hurricane strength as it takes a track very similar to that of Earl for the next few days. Forecasters expect the storm to be centered just to the north of the Lesser Antilles on Wednesday, where Hurricane Earl was early today.

At this point, there are as many questions as answers about Fiona's future.

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Since both Danielle and Earl blossomed into major hurricanes over the open Atlantic when moving through an environment with warm water and little wind shear (upper-level wind flow that inhibits hurricane formation), it might be expected that the same type of intense development would follow with Fiona.

But Fiona has been slower to organize, and government forecasters point to dry air and a lack of organization as factors that will continue to slow the storm's development during the next couple of days. The risk is that Fiona could fight off the dry air in its way and begin to take advantage of the very warm water and develop regardless of the current lack of organization.

In addition, Fiona is expected later this week to move into an environment with wind shear, which could also inhibit development. One of the reasons for the expected shear may very well be Fiona's proximity to Earl in a few days. Since Fiona is moving more quickly than Hurricane Earl -- 24 mph versus 15 mph as of this evening -- the upper-level wind being created by Earl might slow the development of Fiona.

The weaker and less organized Fiona is at the time it encounters shear, the more likely it is to be weakened by shear.

The forecast track of Fiona also carries some uncertainty. Forecasters are confident that the storm will track northwestward -- similar to Earl -- for at least the next few days, and there's a good chance that the storm will remain to the east of the United States. But changes in the overall weather pattern from the weekend and beyond mean that other forecast tracks are possible.

With so many questions, it's important that anyone with interests from the northeastern Caribbean to the United States continue to monitor the progress of Fiona in the coming days.