Cooler air expected in the Northeast, Sally to impact Gulf Coast states

NYC Forecast Briefing: A few sprinkles or showers will move through the area this evening, but the majority of Sunday is now expected to be pleasant. Cooler than normal air will move in to the area for a few days behind a frontal boundary. Additional rounds of cooler than normal air will occur late this upcoming week and weekend. Meanwhile, Tropical Storm Sally continues its trek through the Gulf of Mexico and may impact parts of the Gulf Coast within a few days.

NYC QuickCast

This afternoon: Mostly pleasant conditions and seasonable temperatures are expected. Clouds will increase late. High temperatures will reach the middle to upper 70’s

Tonight: Cloudy with a few showers, especially north of the city. A bit warmer, with temperatures only falling into the middle 60’s.

Monday: Plenty of sunshine, less humid. High temperatures in the middle to upper 70’s with a light northerly breeze.

Northeast US Forecast: Cooler than normal air on the way

Behind a frontal boundary that will impact the area with some showers late Sunday evening, high pressure and cooler than normal air will move into the Northeast states. This airmass will also be characterized by lower dew points, helping the airmass feel refreshing and crisp.

This airmass will last for at least a few days, with very pleasant weather likely as a result. High temperatures for the rest of the week should average in the low to mid 70’s, with plenty of sunshine and very few weather hazards as high pressure dominates.

Temperatures will temporarily warm up again by the middle part of this week. A storm system moving through Southeast Canada and New England will eventually move near the area (likely from Thursday into Friday). A few showers are possible as this system passes by.

More importantly, though, the storm will bring the first really crisp airmass with it. After a front passes the area on Friday, much cooler than normal temperatures are likely next weekend. The last Euro Ensemble suggested temperatures 5-10 degrees below normal, on average, from Saturday into Monday.

Pictured above, a mid/upper level trough is forecast to slide through Southeast Canada. This trough is anomalous in its own right and features some very cool and low dewpoint air. Synoptically, this supports temperatures at least several degrees below normal for a few days in the Northeast next weekend – which matches up quite well with what most guidance is suggesting.

Get your pumpkin spiced lattes ready.

Tropical activity continues to ramp up, Sally a tropical storm

Tropical Storm Sally formed yesterday, and is expected to continue a trek into the northeast Gulf of Mexico today. The storm is currently encountering light to moderate northwesterly shear, which is tilting thunderstorms off to the east of the storms center. This is preventing the system from strengthening too much as of this morning.

The latest shear analysis near and surrounding the storm suggested 10-20 kts (averaging around 15 kts) of northwesterly wind shear. Visible satellite imagery shows that convection is biased to the southeast side of the storm, and this northwesterly shear is likely partially to blame for that.

Sally is also a very broad system, with tropical storm force winds extending quite a bit away from the center. This should also keep the system from strengthening significantly today, at least until the storm can organize a more substantial inner core and tighten up the spatial extend of its maximum wind.

This shear is expected to gradually weaken over the next 12 hours, so the storm may be able to organize itself a bit further. The National Hurricane Center forecasts the storm to strengthen to a hurricane before it makes landfall near the Louisiana coastline on Tuesday.

Most forecast model guidance is now in good agreement regarding the storms track and strength, with ensembles agreeing that the storm will move towards the Louisiana Coast as a Category 1 hurricane. Still, with relatively low shear and warm water temperatures, it is important to keep a close eye on the storms strength and possibly of intensification.

The 06z Euro Ensembles were in generally good agreement in regards to the storms track, bringing the system near the Louisiana coast early next week. Still, some members were stronger and slower with the storm – with deeper pressures indicative of a more substantial system.

Sally is likely to bring multiple weather hazards to the areas it impacts regardless of strength. The system is expected to slow down considerably, which will lead to a high likelihood of torrential, flooding rainfall. Sally remains trapped in a pocket of very moist air throughout the atmospheric column. This means that the system will not have much dry air to deal with, even in the mid levels of the atmosphere.

As Sally approaches the coast, steering flow will weaken and the storm will become “trapped” under a mid level ridge. This suggests that the system will slow down considerably near the Gulf Coast, while tropical moisture pools over the area. As a result, torrential and flooding rainfall is possible.

The Euro Ensemble is strongly suggesting the possibility of prolific rainfall amounts, with the ensemble mean suggesting over 10 inches of rain along parts of the coast. Actual amounts could be much higher than that in areas that receive “training” of tropical moisture – which occurs when areas of heavy rain move over the same regions over and over.

Additionally, some storm surge is possible as the system moves towards the Gulf Coast. The National Hurricane Center is forecast over 3 feet of storm surge in some areas that are highly susceptible to storm surge damage.

We recommend checking out the National Hurricane Center’s latest hazards page and key points in order to help develop a plan for you and your family if you live in those regions.