Sept 30 Night: Final Storm Update

10:00 PM: As the low pressure is now moving inland into North Carolina, from the radar observations, it is becoming apparent that less rain than the original forecast will fall for the area.

From my post earlier this afternoon, it appeared that the forecast could bust, as despite the models still indicating 3-5 inches of rain for the area, the observations suggested otherwise. The latest model trends and the observations continue to support my thoughts that rain totals could end up significantly lower than the original forecast for the storm due to an unexpected turn in the storm set up.

What Is Going Wrong?

I’ll have more on what went wrong with the forecast with a post tomorrow about this storm and reviewing what happened, but I’ll give an explanation of what went wrong so far and could go wrong tonight.

The first low pressure ended up moving further inland than expected, which combined with a sharper cut off than some models expected, led to a dry yet windy day for the area. The second low pressure was supposed to start turning north then NNE, moving just off the coast and slightly east of NYC, as the cold front from the first storm would push the storm further east, however that has failed to happen so far, and as with the first storm, the second storm is currently pushing more inland than expected, and is still moving NNW. By 8 PM, the models from earlier today already had the storm moving NNE, with heavy rain starting to fall in NYC, however it is already 10 PM and this has failed to happen.

The storm will continue to move NNW then north, and will eventually be forced to turn NNE due to the cold front, which will move east, bringing heavy rain to at least parts of the area, however most of the heavy rain will stay to the north and west of New York City, as the low pressure moves just west of New York City. Due to this, however, strong winds can be expected in Long Island tonight, with gusts up to 60 mph possible, with lighter but still strong winds for the immediate NYC area. Only the interior parts of the area (NW NJ, Orange County in NY) will see the very heavy rain.

Rain Forecast:

With the above said, I posted my rain forecast to the left. The right end of the dark green zone could be a little east of my forecast, but for now these are the main boundaries I am using.

For the dark green zone, expect a steady heavy rain for most of tonight into tomorrow morning, with a total of 3 to 5 inches of rain expected. Rainfall amounts could be locally higher in heavy rain bands.

In the green zone, expect 1 to 3 inches of rain, with at least 1 to 1.5″ for NYC, if not a little lower in the drier case scenario. By the time that the storm is nearing NYC, the rain will start to move more eastward, but likely in the form of a moving line of heavy rain, not a stalled heavy rain line that the central Mid Atlantic has seen all day and NW NJ/eastern PA will likely see tonight.

In the light green area, expect generally less than 1 inch of rain. The rain will be in the form of moderate rain moving NE, and while the rain will be relatively light, strong wind gusts will be the main concern, with gusts up to 60 mph possible.

Note On The Forecast: The above is my current thinking, and is based on my thinking and the RUC short term model, that has been catching on to this trend. Rain totals can still end up slightly different than my forecast, especially if another unexpected turn happens, but for now this is my thinking.

Before the storm, I said that this could be a damaging storm and cause significant impact on the area, and while that did not happen yet, because of the storm being further west it has had a significant impact on a line from eastern Virginia through eastern Maryland and Pennsylvania. In that area, between 8 to as much as 12 inches of rain fell so far, and rain is still coming down. These places are likely to break records for the most amount of rain in 24 hours, and there is significant flooding in those areas. Had the storm not been this far west, we could have been dealing with the same effects in the NYC area.

I will post a summary of this storm tomorrow, with a brief forecast for the next few days, but the next full update will be posted on Saturday.

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