MIAMI (CBS4) — From CBS4 Meteorologist Craig Setzer…

Isaac continues westward as a large, but weak tropical storm. It’s time we start talking about what we will be looking for in the coming days as an indication of how bad our weather could potentially be.

One thing to watch between now and Friday night will be where Isaac crosses Hispaniola and what direction it’s moving after it crosses. This factor will play a significant role in how bad the weather will be in South Florida and the Keys.

David, Lissette, Jeff and I look at a number of potential paths, called spaghetti plots. Here is an example from our CBS4 tropics page. Each colored “spaghetti noodle” represents a computer model’s potential path for Isaac.

There are three scenarios for Isaac: it takes a rightmost path, a central path, and a leftmost path.

Rightmost path. This would be of greatest concern to us because the storm would make a closer approach, meaning the core and its stronger winds might be felt here. Also, it would spend more time over water (between Florida and Cuba), providing a longer window of opportunity to significantly strengthen before reaching us.

Central path. This would most likely keep Isaac over Cuba, limiting its potential to strengthen.

Leftmost path. This would keep the storm’s core far away from us, a best-case scenario.

So what will I be watching in the numbers?

The hurricane center puts out a text product called the PUBLIC ADVISORY or TCPAT4. This product has the direction of movement of the storm in degrees, like on a compass. 270 is exactly west, 315 is exactly northwest, etc. It reads like this:

PRESENT MOVEMENT…W OR 270 DEGREES AT 13 MPH…21 KM/H

I will be watching to see what direction Isaac is heading as it gets to Hispaniola and Cuba. I would like to see 290 degrees (slightly north of exactly west). I will be concerned if the number is over 300 degrees (exactly west-northwest).

The reason is this: the coast of Cuba runs about 300 degrees (exactly west-northwest). If Isaac is moving to the right of 300 degrees (closer to north), it will reach the warm water sooner.

Finally, the center path may be academic as the storm’s envelope (how far Isaac’s winds/heavy rain extend from the center) is very large and Isaac may to an extent be able to straddle Hispaniola or Cuba.

This land encounter would likely limit strengthening but it would likely survive the mountainous northern Caribbean Islands.

>> Visit the CBS4 Tropics Page for an interactive Tropical Tracker, the newest computer model tracks and more.

>> Here’s how to use the CBS4 site to prepare for and monitor Isaac: