Isaac grows stronger; Tampa to Mobile Bay “forecast cone?”

Just west of Tampa Monday PM GFS model forecast for Hurricane Isaac

Near Mobile Bay at 10am Wednesday European Model forecast for Isaac landfall

Isaac still a threat to Florida - Including the Keys, Miami, Fort Myers/Sanibel and Tampa

Weekend split for Minnesota - Sunday looks like the nicer day

Source: Twin Cities NWS

Forecasting Isaac: A complicated storm

Forecasters at the National Hurricane Center are growing some extra grey hairs this week.

When it comes to forecasting hurricanes, Isaac is proving to be a challenge. Here's why Isaac is a complicated storm.

1) Multiple centers: Isaac has shown more than one circulation center over the past 3 days, making a fix on his position difficult. This is important because the models need an accurate "initial" location of the center of Isaac to generate a more accurate track.

2) Late bloomer: Isaac has been slow to develop, and has lingered as a tropical storm for 2 days now. Because of this it's tougher to get a sense for how well organized Isaac will eventually get. It's been tough to get a read on Isaac's eventual storm geometry.

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Source: NOAA

3) Tough terrain: Isaac's probable forecast track takes the circulation through some high mountains in Haiti and eastern Cuba. That makes it difficult to know with any certainty how strong Isaac will be when it eventually emerges into the Florida straits Sunday or early Monday.

4) Dueling models: Two of the most accurate hurricane forecast models continue to be at odds over Isaac's eventual track.

The GFS insists that Isaac will track through south Florida & the Keys, and will be close enough to Tampa to be a player there Monday.

Source: WxUnderground

The European model (usually the most accurate) has consistently held the western track, and steers the storm into the open Gulf away from Tampa toward Mobile Bay.

Source: WxUnderground

The bulk of other forecast models lie in between these two solutions.

Source: http://www.sfwmd.gov/sfwmd/common/images/weather/plots/storm_09

A shift of even 50 miles could mean the difference between "no big deal" in Tampa and "hurricane conditions."

Let's hope the GFS and Euro come together on an accurate track this weekend.

Minnesota Weekend Forecast: Split decision

Thursday night's sky & lightning show was impressive.

Source: Twin Cities NWS

The heaviest storms formed and boomed west of the metro. There were a few damage reports, as you can see from the NWS summary below.

Source: Twin Cities NWS

The next frontal system pushes in Saturday, with another chance of scattered T-Storms. So far SPC has not issued and "risk areas" for Minnesota, but I can't rule out an isolated severe cell or two late Saturday PM & evening.

Source: NOAA via College of DuPage Weather Lab

Sunday looks like the sunnier nicer day this weekend.

Enjoy!

PH