A complicated pattern awaits – Stormy for most of the Northeast
After a relatively tranquil September, it appears we are heading into interesting times when it comes to the weather pattern in the Northeast, and we are locked into a stormy, messy pattern. Not one, but two tropical systems are the main players, along with a frontal boundary which is expected to become trapped in the region. All in all, it means lots of rain, wind, high waves and possibly coastal flooding for many areas with multiple threats. This shouldn’t be an extreme event like Irene or Sandy, but it will not be pleasant, that is for sure.
Tropical Depression Eleven
The first factor in this forecast is a newly formed tropical depression located to the northeast of the Bahamas, well to the southeast of the Carolina coast. It is forecast to intensify into Tropical Storm Joaquin later today and track northwest for the next day or two, then turn northward roughly along the 72W to 75W longitude axis until merging with the frontal boundary late this week before it can make landfall. A blocking ridge to the east along with a developing cutoff low to the northwest should force the system inland, either before or after merging with the front.
The reliable global models generally keep this system weak with few showing more than a moderate tropical storm. The mesoscale models are much more bullish, but they have a poor record of reliability in the higher latitudes. The GFDL shows a surprising solution in that Joaquin makes landfall on central Long Island as a low-end Category 1 hurricane on Friday afternoon and maintains storm intensity into the northern areas late Friday. The HWRF is even more bullish, showing a Category 2 or 3 hurricane offshore of Cape Hatteras weakening to a Category 1 as it makes landfall near Block Island. Both are very unlikely scenarios.
Gulf of Mexico low
A second tropical low is currently located in the central Gulf of Mexico and is slowly moving northeast. It has been tagged as Invest 99L, but development into a tropical cyclone isn’t particularly likely (the NHC gave it a 30% chance this morning, which might be generous given the very high shear in the area, although shear is lower near Florida). The main impact from that system will be heavy rain in the Southeast this week before it is absorbed by the systems above.
Northeast weather situation
Combining the frontal boundary with two tropical features will almost certainly result in a very wet stretch of weather in most of the Northeast. The Weather Prediction Center suggests that rainfall totals of 3 to 6 inches will be widespread from Nova Scotia to Virginia and west to the Appalachians, and (in my opinion) this could be a conservative forecast given the atmospheric moisture and lift available. Some models show over a foot of rain for many areas! Thankfully, soil conditions in the region are near normal to drier than normal, so a situation like Irene and Lee in 2011 with catastrophic inland flooding isn’t particularly likely unless the high end rain totals verify (such as with the Nashville flood in 2010), but flooding remains a significant concern. In August and September 2011, the soil moisture in the Northeast was at near record levels, which attributed to the extreme flood event despite lower rainfall totals.
When it comes to wind, confidence is much lower in terms of impacts. As long as the systems remain weak, the wind impact should be minimal at best. However, immediate coastal areas may see wind gusts of 35 to 45 mph late this week. Obviously, if the mesoscale models verify and a strong tropical storm or hurricane makes landfall, winds would be much greater and conditions much more severe. However, that is not likely at this point. Inland areas shouldn’t see much wind impact unless the system is stronger than forecast. Isolated severe weather is not out of the question ahead of the frontal boundary and in heavy rainbands as well, but we are too far out to forecast specifics there.
Some of the greatest impacts will be in coastal areas and out at sea. Given the long wind fetch and pressure gradients, very high seas are likely all week offshore of the Mid-Atlantic and Northeast coasts. Specific details cannot be determined at this time, but it would not be surprising to see wave heights as high as 15 to 20 feet in the northwestern Atlantic accompanied by gale to storm force winds. Coastal erosion is very possible along the entire coastline, especially in areas that get a direct onshore flow. Some storm surge flooding is also possible, depending on the strength of the storm, the timing and the wind direction. However, an extreme surge event like Sandy doesn’t appear likely right now.
Confidence in forecast
- Track – Moderate to High
- Intensity and structure – Low
- Rainfall and flooding – Moderate to High
- Wind – Very Low
- Severe weather – Low
- Marine impacts – Low to Moderate
This will not be a pleasant week for weather in the Northeast. Except for areas far inland (i.e. closer to the Great Lakes), very heavy rain is likely along with multiple coastal storms associated with a frontal boundary and tropical cyclones. There is also a slight chance for a significant tropical cyclone landfall. Fortunately, the antecedent conditions aren’t conducive for major flooding unless the high-end rainfall totals occur. It remains to be seen what happens but we should be prepared for everything possible.
Forecaster Craig Ceecee