August 23: Post Storm Review, Look At Week Ahead

Today’s update was put in two parts, both in this post. The first part of this post is about yesterday’s storm and looking at the forecast for it, and the second half is the discussion about this week and the weekend, as well as Tropical Storm Danielle. I also added a poll to the right below the radar about what next week could bring to the area, for those who want to vote.


Yesterday’s storm is mainly over for the area, though there are still scattered showers around, mainly northwest of New York City. Looking at the radar estimates, heavy rain did fall across most of the area, with over 1.5 inch for most of the area, except for Long Island. The heaviest rain totals in the area ended up over northwestern Bergen County, NJ, into Rockland County, NY, where rainfall amounts were as high as 5 inches. Long Island, however, ended up with the lowest totals, with rain amounts generally between 1/2 and 1 inch, locally higher towards western Long Island.

Post Storm Review: What Happened?

Yesterday’s storm was one of the most difficult storms of the year to forecast. Even up until the day of the storm, there was a lot of uncertainty, with the models showing a wide range of solutions up to the last minute. There were some things that were likely to happen, such as the heaviest rain focusing in central New York as well as heavy rain falling in the area, but there also was a lot of uncertainty, such as where the secondary low pressure tracks, the location of the heavy rain axis for the area, and whether the heavy rain offshore would move inland as the models suggested to bring southern New England a round of heavy rain, which did not happen.

Below, I posted a comparison of my forecast rain totals and a rough estimate of the actual rain totals, looking at the radar estimates. The estimated rain totals could be slightly off for some places, but they give an idea of how much rain fell.

What was right: The map did get some parts correct, such as the heavy rain staying south/west of Boston, and SW Maine only seeing light rain, which was a difficult decision to make based on the models. For example, one run of the NAM model showed barely an inch of rain for Boston and a little rain in SW Maine, and the next run showed nearly 5 inches of rain in Boston and over 2 inches in SW Maine. The 1 inch line that ran through northern New Jersey verified, as most places south of that line saw less than 1 inch, though most of Long Island saw less than 1 inch. The forecast for the 2+ inches area to mainly stay N and NW of NYC was also correct.

What went wrong: The rain was lighter across PA and central/southern NJ than expected. I noticed that by the early afternoon hours, when there were only scattered storms around and it appeared that due to the clouds clearing in Pennsylvania behind the strong storms, there wouldn’t be heavy rain overnight (behind the storm line, that was supposed to move through during the evening) for PA and parts of New Jersey.

The forecast for Long Island also did not verify. The models suggested that heavy rain would form offshore and move inland overnight, bringing a round of heavy rain. The heavy rain did form, but instead it went out to sea, which I noted as a possibility in the storm scenario update I posted yesterday afternoon. While it also appeared that Boston wouldn’t see very heavy rain, they still saw much less rain than expected, as most of the rain bands were unable to reach them, and instead dumped heavy rain in other parts of Massachusetts and Rhode Island. Northeastern NJ and SE NY also ended up with more rain than expected.

Summary: This was a very difficult storm to forecast, and there were a lot of parts that I missed in my forecast, but there were also some parts that I got right as well. It did become apparent that some parts of the forecast would be incorrect several hours before they happened, showing that making last minute forecasts based on the observations is important in cases where there is uncertainty up to the last minute.

Today’s Update: Cloudy And Chilly Week, But Warmth To Return

The rest of today will be cloudy and chilly with isolated showers, locally heavy, with a NE wind. There could be gusty winds in Long Island and near the coast. High temperatures will be in the upper 60s to lower 70s inland, lower to potentially mid 70s for the immediate NYC area, and in the upper 60s to lower 70s for Long Island and S CT.

Tonight will be cloudy, with low temperatures in the lower to mid 60s for S CT, mid to upper 60s for Long Island, in the lower to mid 60s for the immediate NYC area, and in the upper 50s inland. Tomorrow will be another cloudy and chilly day, with high temperatures similar to, if not slightly warmer than today’s, with an ENE wind expected. Windy conditions are possible along the coast again.

A low pressure will pass to our east on Wednesday, however it will keep the cloudy and chilly conditions around, along with some showers. This low pressure will bring steady light to moderate rain for eastern New England, with the highest rain totals in Maine, but these totals won’t be as big as they were with yesterday’s storms.

Some models keep the low pressure close to the area and bring a widespread 1 to 2 inches of rain for the area, and while this is unlikely at this time, this solution will be watched in case it becomes likely.

Longer Range Outlook: Cooler Weekend, Heat Could Return Afterwards

By Thursday, a colder air mass will approach the area, though temperatures will be warmer, with high temperatures in the lower to potentially mid 80s ahead of the colder temperatures. By Friday, though, the cold air mass will be over the area, with much cooler temperatures. High temperatures will likely be in the lower to upper 70s across the area, with low temperatures in the 50s for most of the area, except for the immediate coast. The interior areas may potentially reach the upper 40s.

Starting Sunday or Monday, however, the models are showing a high pressure near the area, which will also block Danielle from affecting the East Coast (more details on Danielle are below), and this is expected to bring a much warmer air mass into the area. There is uncertainty on how warm the air mass is, but there is the potential for temperatures to reach the 90s again for parts of the area.

I added a poll in the top right corner of the website below the radar about next week, about whether next week could feature temperatures below, near or above average temperatures, or a heat wave. Vote your thoughts on next week in the poll, which will close on Friday. More details on this will be posted tomorrow, as well as a detailed discussion on Danielle.

Hurricane Danielle: Potential Major Hurricane To Stay Offshore

Tropical Storm Danielle is currently a strong tropical storm in the eastern Atlantic Ocean, and is moving WNW. Danielle is currently located under a favorable environment, and is expected to strengthen into a hurricane within the next 12 hours. Afterwards, there is uncertainty on how favorable its environment is, but if it can stay under supportive conditions, it may strengthen into a category 3 major hurricane. A category 4 hurricane is unlikely at this time but is not out of the possibilities.

Danielle, however, is unlikely to affect the East Coast. In a few days, while there is a trough near the area, there will be two high pressures, one near Bermuda and one in the east central Atlantic, which will allow Danielle to move in between. This will also force Danielle to turn more NW, and a high pressure near the area by early next week will block Danielle from approaching the area, forcing it to turn north and then NE. It may threaten Newfoundland in Canada, otherwise it should stay away from land.

A more detailed discussion on Danielle, as well as a map, will be posted tomorrow.

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