Plaincast

What has changed

No significant changes made with the latest forecast.

Messages

Showers and thunderstorms today for NYC and north and west. An isolated severe thunderstorm is possible.

Unsettled weather expected Tuesday through Thursday due to a slow moving low pressure system. Heavy showers and thunderstorms will bring the potential for flash flooding, mainly Tuesday afternoon through Wednesday.

Potential for minor coastal flooding mid to late week with a coastal low.

Discussion

.KEY MESSAGE 1. The stretch of dry, pleasant weather looks to end for some today. Several weak shortwaves will move through the mean upper level trough over the area. There is decent agreement that the western half of the area is able to destabilize to about 1000-2000 J/kg of MLCAPE. This could lead to isolated to scattered showers and thunderstorms for NYC and north and west. Shear looks to be weak, so this will be more of a pulse storm environment. DCAPE is progged to peak around 500-600 J/kg, so an isolated damaging wind gust can not be ruled out. The SPC continues the marginal risk of severe weather for NYC and north and west. While pwats are expected to only be around 1.5 inches, a long skinny storm energy profile and slow moving storms will likely result in isolated heavy downpours. A quick inch in an hour can not be ruled out. This will likely result in more of a nuisance flooding than a flash flood threat.

.KEY MESSAGE 2. The threat for a more substantial rainfall/flood event will come Tuesday into Wednesday. Within the mean upper level troughing, a strong shortwave is progged to dive down towards the area on Tuesday and become closed off Tuesday night. There is great agreement with the 00z global guidance that this closed upper low is centered over or near the area Wednesday through at least Thursday, before gradually shifting northeast Thursday night. There are still difference with how the global guidance is handling the surface low/potential secondary low. The the regional model continues to be the outlier showing a stronger low centered to our south. Regardless, heavy rain can be expected, but exact location is still uncertain.

Now while embedded convection is likely with a moderate to heavy rainfall at the onset, a low track to the south of the area will keep the airmass more stable, with a better chance of a stratiform rain as we get into Wednesday. Even so, deep moisture and an anomalously deep low, will make for very efficient rain processes. The flood threat could transition to more of a long duration versus flash flood threat. WPC has the area in a slight risk of excessive rainfall during this time.

The rainfall forecast generally remains unchanged at this time and ranges from 1.50 inches across eastern LI/SE CT, to 2 to 3 inches across the rest of the area. Hourly rainfall rates are more of question based on the low track and how unstable the airmass gets. The heavy rainfall axis will likely fluctuate the next couple of days and it is too early to be specific with rainfall amounts. However, know the ingredients are there for a significant rainfall.

.KEY MESSAGE 3. With the approach of a full moon midweek and an onshore E/southeast flow with low pressure passing close by, minor coastal flooding is a possibility. There is still a fair amount of uncertainty at this time. Latest forecast brings some of the south shore back bay locations of LI and western LI Sound to just below minor coastal flood benchmarks during the evening/nighttime high tide cycles.