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August 2018

When you think back on the weather of August (and the summer) of 2018 what will you remember most? Likely not much as our weather memory tends to be very short, and recency bias tends to skew our perception of recent events. Here is some context for Islip, NY along with some (hopefully) helpful charts.

August Mean Temperature: 76.7 F (+3.9 F and 4th warmest since 1964)

August Precipitation: 6.15" (+2.17", 10th wettest since 1964)

Summer Mean Temp: 73.5 F (+1.6 F and tied 5th since 1964)

Summer Precipitation: 12.94" (+1.31", 20th wettest since 1964)

Quick Background

Over the past few months I have been working on a few different charts that track hourly weather variables for Islip, NY. They were a lot of fun to make, and I find them to be valuable for visualizing local (for me) weather conditions. While not all of these conditions observed at Islip are representative of the region as a whole, they do offer good regional insight in some cases. Local microclimates, and other regional differences in observed weather are items that I will discuss from time to time where necessary. I hope to share monthly summaries similar to this one on a regular basis going forward.

The hourly charts came about because of an idea I had about a way to display cloud cover that could somehow capture the feel of the day. After a few weeks of messing around with different displays I started playing around with tracking wind, then dewpoint, then eventually temperature using a similar process. In part, this post will serve to explain what the charts show and how they might be useful.

Before I jump in, I do want to mention the value in simply paying careful attention to observations as a way of learning. I have been paying fairly close attention to weather for decades, but never have I taken so much care to consider each hourly observation at one location to the extent that I have over the past few months in creating these charts. It’s a great way to observe patterns and phenomena that occur on daily and hourly scales, and gain new insights that almost inevitably lead to new questions or ideas (and probably new charts).


The big story during August 2018 were the persistently high dewpoints that set many new records, not just for Islip, but throughout the northeast.

It took Islip a record 23 August days to record a dewpoint temp below 60F. This was 5 days later than the previous latest occurance in 1984.

Here's what the hourly summary charts for both August and climatological summer looked like at Islip, NY. A typical gauge for discomfort would be a dewpoint of around 70F. It's around this number that the color scale becomes predominantly blue, and you can see there was plenty of blue this year. Ultimately, it would be cool to have anomaly data for dewpoint as well, but climatology for dewpoint is difficult to come by, and would likely require a whole other project.

As you may notice on the summary chart, there were an inordinate amount of 76F dewpoints observed this summer. Covered this on twitter...

Some additional context on the extent of the record levels of humidity this summer (as quantified using dewpoint temperature). Comparing the total number of hours at or above the 70F threshold we can see that 2018 surpasses all previous years (back to 1973) by 168 hours or exactly 7 days! That's a full week more discomfort than the previous record, and over two weeks more than your average summer.

Upping the threshold to oppressive levels of dewpoint at 75F plus, we find more of the same. 64% more hours at or above this threshold than the previous record for the month of August. Just amazing persistence in our weather pattern during our typical climatological peak for humid weather- incredible results.

Cloud Cover

This is where my work on the hourly charts began. The seed for this idea came from my desire to to create a cloud climatology visual for Islip (or any city really)– something I still intend to do. Unfortunately, useful cloud data is not easy to find.

Hopefully the color scheme is intuitive; yellow boxes represent sunnier skies and gray boxes cloudier. There are 5 different possible sky conditions reported hourly. In order of increasing cloudiness they are; fair, a few clouds, partly cloudy, mostly cloudy, and overcast. As such, this chart only displays 5 distinct colors depending on the hourly report. Total hourly counts for each type of sky cover observation are shown in the "summary" in the upper right corner.

Since August is the final month of climatological summer, here is the full summer chart as well.


As is typical during the summer months, wind is not a major factor other than normal diurnal oscillations. Most days, absent a strong synoptic system producing a strong pressure gradient, the strongest winds will be observed during the warmer part of the day and calmer overnight. Ultimately the air moves because of energy from the sun, and this is a small example of that.

The very beginning of the month did feature some stronger winds with a synoptic-scale weather system that ushered in a pattern change to bring more significant tropical humidity to the region.

The late July (22-23) out-of-season nor'easter shows up nicely on the full summer version of the chart. This one should be more interesting as seasonal transitions begin to become more prominent in Autumn.

To illustrate how much different this chart looks in different seasons. Here's an example from January of this year. Notice how much more colorful things become during the cold season when there's a much more significant battle taking place in the middle latitudes. Our strong early month blizzard is easy to locate.


I was originally uninterested in creating an hourly temperature chart, but am really happy that I ended up doing it. The diurnal and day to day changes make for a much more dynamic look than the dewpoint charts. One thing to note here is the pretty decent break in the pattern that showed up in the 3rd week of August (between around the 20th-26th). You can see some greens showing up in overnight lows that will grow in number through September as nights become longer and our seasonal transition begins to accelerate.

The clear skies and drier atmosphere allowed for the reemergence of our local microclimates. Noted this in a late August tweet:

Also cool to see a side-by-side comparison of some of the local observations sites- from NYC to Montauk, with Westhampton Beach stealing the show as usual. Overall, a great example of radiational cooling and typical microclimate differences observed under clear skies and calm winds. Note the precipitous drop in temp at FOK after sunset, and then the subsequent rapid rebound after sunrise the next morning.

Again, here is all of climatological summer 2018. This was not a summer of very high maximum temperatures, but as discussed earlier, the extreme dewpoints sure made much of it uncomfortable, and kept overnight lows above normal. Who knows, maybe next summer there'll be a heat index version of these charts.

One last thermal chart to summarize the month of August. I have been making these for a while to track monthly anomalies, and the portion of which is made up of high temperature vs low temperature anomalies (red and blue bars respectively). The yellow dots are average daily anomalies and the dashed line tracks month-to-date anomalies. Again, the week-long reprieve stands out. Let's call it the anomaly within the anomaly chart.

Happy autumn.

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