Great Lakes Water Temperatures

[jimh]

Our summer cabin is on the shore of Lake Michigan, not on the open lake but on Grand Traverse Bay near Northport, in the south end of Northport Bay. We look forward to being able swim in the Summer in water temperature of 70-degrees-F or slightly higher. This summer swimming has been quite a challenge. The peak water temperatures we have been seeing are barely above 70-degrees-F, maybe 72-degrees-F at best. That is the surface water temperature near shore.

NOAA Great Lakes Environmental Research Laboratory publishes surface water temperature charts, and below in Figure 1 is the chart for today, September 3, 2023:

Fig. 1. NOAA/GLERL chart for Lake Michigan for September 2, 2023. Northport is in the northern part of Grand Traverse Bay.

lakeMichiganWaterTempCrop.jpg (47.13 KiB) Viewed 2502 times

The graphic above is showing surface water temperatures at our location as 16-degrees-C or 61-degrees-F. I am sure the water is a bit warmer near shore in the five-foot depths where we are swimming, but on our last swim, yesterday, with air temperatures finally in the high-70-degrees-F range for the first time in weeks, the water did seem extremely cold. Perhaps several weeks of cloudy weather and overnight low temperatures in the high-50-degrees-F range have contributed to the cold water in the lake.

Generally, sometime in the first two weeks of September the water temperatures (and the air temperatures) decline to the point at which we just have to give up open water swimming. We are hoping this year we can swim at least another week or two.

I mention this because here in the northern half of the northern hemisphere--our latitude is just a bit more than 45-degrees-North so technically we are closer to the North Pole than to the Equator--we normally don't have blisteringly hot summer temperatures, but we do get the occasional 80-degree-day at some point during Summer. I don't think we have hit that yet this year in Northport.

[jimh]

No sooner than I had mentioned the lack of an 80-degree-day, we got one. Yesterday Northport hit 83-degrees-F, and that was the hottest day so far, to my knowledge. But today, Monday, September 4--Labor Day--the forecast is calling for 90-degrees-F. If that happens it will certainly be the warmest day of the Summer.

ASIDE: we did get in a nice swim yesterday, but the water temperature was rather cold, perhaps in part from the big difference from the air temperature. I did not measure the water temperature, but we had to get out after about 30-minutes of swimming due to getting very cold.

[jimh]

The 90-degree-F air temperature never arrived on Labor Day, but it was a very nice day, sunny, about 80-degrees, giving us two days of back-to-back Summer weather for the first time. It was so warm that the cabin got up to about 78-degrees indoor temperature, so I ran the air conditioner for several hours to cool off the place and reduce indoor humidity. This was only the second time all Summer the air conditioner had been run. It was not completely necessary to run it at either date, but I look at the air conditioner as something that needs a bit of exercise now and then to keep it in working order. So a few hours of running once a month perhaps should keep it happier than sitting unused for two years.

The warm spell is gone, and mid-day temperatures are now in the 60-degree-F range, skies are very clouding, there is a strong East wind, thunderstorms, lightning, and very heavy rain. The rain was welcome, as rain so far this Summer has been sparse in our location. Storm fronts seem to always be passing just ten miles south of us.

The little heat wave continued into Tuesday September 5, 2023. I hope the nice swim he had that day won't be the last one of the year. The weather was a marvelous combination of super clear blue cloudless sky, warm air, cool water, and barely any wave motion, and we relaxed and swam for almost an hour. That was the Summer weather we had been hoping for all season.

[Don SSDD]

Jim, in Mahone Bay, Nova Scotia, eastern Canada, within say 1-1.5 miles of shore, I’ve seen 80-degrees-F in 10 to 30-feet depths. We’ve had maybe 30 days above 75-degree-F air temperature, and it’s raining and 72-degrees-F here now.

I was out in the Whaler on Friday with the water temperature consistently 76-degrees-F. I haven’t seen the water temperature below. below 70f since early July.

[jimh]

Don--thanks for the temperatures from a warm bay on the east coast of Nova Scotia that is open to the Atlantic Ocean. You must be getting a curl off the Gulf Stream up there.

This last weekend, Saturday (September 9) was a bust; at the local boat launch ramp at 11 a.m. there were ZERO boat trailers in the parking lot, indicating no one had launched a boat. Normally on a Saturday morning the parking lot is full by 9 a.m.--that is how cold the weather was. But by 3 p.m. the sun had been out for a while, the wind dropped to very light, the air temperature was about 70-degrees-F, and I decided to take a chance at swimming. I intentionally did not check the water temperature because I did not want to prejudice my desire to get in a good swim. The water was cool, but tolerable. I got in a good 30-minute swim, but I stayed in shallow water close to shore because it was definitely warmer than water in 6 to 8-feet. I think that may have been the last swimming of this year--unless we get a real heat wave for Indian Summer and the water temperature holds up. The secret on Saturday was there had been very light West wind for two days, and for us (on the east side of the peninsula) that means almost no wind at all, and no wind waves coming into the shore. So the water was not getting stirred up, as occurs with wind with any East component.

Sunday (September 10) was too cold, too windy, too rainy, and this morning (September 11) it is colder, more wind, and more rain.

The forecast for this coming Saturday looks encouraging, so maybe one more swim is in store.

Another indicator: on Friday night I noticed there was line of eight sailboats sitting on moorings about a mile north of me. I was wondering if there was some sort of sailing rendezvous going on. But later I figured out the cause: they were abeam the boat yard and were getting in line to be hauled over the weekend.

[Don SSDD]

We have some neighbours who swim from May/June to early October, 2 who did so almost every day until into their early 90’s. The Bay is protected by a reported 365 islands, they help reduce wind and waves. Our water around here runs 30-90 ft depth.

I’m from Prince Edward Island, I’ve been on the north shore there with salt water in the 80’s, and their South shore is more shallow and warmer. Their beach sand is a dark red when wet, really draws the sun.

[jimh]

Here in Northport the overnight low temperatures have been much colder than the water temperature, which I infer will lead to cooler water. This morning the air temperature was 48-degrees-F. Although it warmed up to 70-degrees-F by afternoon, I was not ready to test the water by swimming. I did spend several hours working outdoors in the moderate temperatures on various projects. We may get the boat in the water this week, as more 70-degree-F days are forecast, but I am not sure I will be swimming any more this year, at least not in Lake Michigan.