Let’s Use Arthur As An Example


There’s a lot packed into the map at the top of this entry (click for a larger view). Don’t be overwhelmed. It’s pretty easy and I’ll break it down.

What you’re looking at is a history and prediction of Tropical Storm Arthur. This is based on the GFS, not usually a great hurricane model, but this isn’t a particularly tough forecast.

Hopefully you see the Eastern US and Canada. The colored areas represent ocean water temperature. It’s done in degree Celsius.

Arthur is in an orange area corresponding to 28&#176-29&#176 Celsius. That’s basically the low 80s&#176 Fahrenheit. Up to North Carolina there is relatively warm water. North of that water cools rapidly. Off Cape Cod it’s 17&#176-20&#176 Celsius or mid-60s&#176 Fahrenheit.

That colder water will quickly shut down the tropical characteristics of any early season storm. Arthur, interacting with a front, will be more a rain than wind maker for most of the Eastern Seaboard. The brunt will be felt in the Northeast Friday, what looks like a pretty crappy day.

The boxed numbers with balls in between forming a line is the storm’s track. The number in the box is the date. You’ll notice they’re bunched up around Florida, but spread out beyond the 4th of July. That shows the storm’s forward motion increasing rapidly.

The faster the forward motion, the easier the track is to predict! That’s one reason I’ve been so blase about this storm’s chances of impacting the Northeast. It’s fast moving and very likely to stay offshore.

Thanks to Dr. Robert Hart of Florida State University for providing the map (I actually haven’t asked him yet, but he won’t say no.)

7 thoughts on “Let’s Use Arthur As An Example”

  1. Well done .. Nice to have you watching our backs as usual!! At least here in saybrook ct it looks like rain/showers much needed tho… Thanks again

  2. Thank you for posting this! It is wonderful to have someone that can take what looks so complex and translate for those of us who are fascinated by the weather but lack the background or training to figure it out.

  3. Thanks Geoff! We still miss your lessons in meteorology, astronomy, vegetable gardening, etc. You were the best meteorologist that CT ever had!!!

  4. Looking at the water temp maps…I always thought that our local area (Long Island, Connecticut, New Jersey) coastal waters where the true dividing like between the cold New England/Canadian Marirtime waters that start near Cape Cod….and the warmer subtropical waters that begin near Delaware Bay and go south to Florida.

    The University of Florida Map is nice – but here is a much more detailed (and contoured!) map of SST. You can see that right around Cape Cod SST are currently near 17 C (65 F) and cool quickly to 13/14 C (54 – 55 F). Yet, as soon as you get south of New England/Cap Cod – SST shoot up fast. Right now SST are 22 C (72 F) off Long Island and quickly shoot up past 25 C (75 F) and to 26 C (80 F ) off North Carolina.


    What’s even more interesting…. is that we think of SST of 16 or 19 C (60- 66 F)as cold….yet right now 90 % of the coast of California has SST below 18 C. In fact, as the image shows, even the coastal waters in southernmost California near San Diego and south of LA are only about 20 C (68 F), actually cooler than off Long Island NY where it’s 22 C (70 F) – even though NYC is 400 miles or so south of southern California. What’s even more shocking is down along the South Carolina coast (near the same latitude as southernmost California) SST are 28 C (82.5 F).

    It’s amazing how warm the currents are in the Atlantic and cold they are in the Pacific


  5. I have and ever shall trust your expertise in this Geoff. When something is happening or will happen, I look to you for clarification. I just can’t have faith in the young’ens they lack your experience.

  6. While I think you might be right, that tropical cyclone development normally occurs south of Cape Hatteras…many tropical cyclones can mainatain hurricane intensity north of Cape Hatteras until around the south shore of Long island/coastal NJ/CT. I think once hurricanes get near and north of Cape Cod they will always lose intensity because the Labrador Current goes as far south as eastern Massachusetts.

    My real point was how the coastal waters are so much warmer on the East Coast than the West Coast. I think those chilly Pacific waters are responsible for the fact than few if any hurricanes have ever hit the California coast…while we on the East Coast see to have a tropical connection so to speak – lol.

    As far as the weather today here on the East Coast – it certainly felt tropical, temps were in the upper 80’s to lower 90’s from Virginia Beach, VA to the NYC/CT area, while dew points were in the lower 70’s F. Still, I love every minute of it, feels like I’m in the Caribbean.

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