October 2017 - Page 4 of 5 - New York Metro Weather

Cooler Conditions Finally Take Over, But Will They Last?

October 16, 2017/by Steven Copertino

Good Evening!

A cold front moved through sections of the Northeast late last night, bringing areas of showers, gusty winds, and more importantly a sizable airmass change. Within a period of only a few hours, the cold front knocked us into more autumnal conditions, with dewpoints dropping from the unusually high low to middle 60’s, back into the low 30’s-leading to a much more crisp feeling to the air today. Additionally, cooler temperatures aloft have left the entire area with much cooler highs as well, with most of the Northeast seeing highs in the middle 50’s to lower 60’s, with even a few areas in Pennsylvania and New York seeing temperatures stuck in the upper 40’s. Conditions have also become quite windy across the area behind the cold front-with many stations reporting northwesterly winds gusting in the 20-30 mph range through the afternoon and into the early evening hours. This northwesterly flow has also worked to bring in cooler air over the relatively warm Great Lakes, which has generated some lake-effect clouds this afternoon that has mainly been focused over New York state, with some low-topped cumulus clouds over Pennsylvania. Further east over the metro area, we’ve seen a mix of sun and clouds over the area as some trailing upper level cirrus clouds quickly move from southwest to northeast on the eastern side of the upper level trough.

As we head into sundown, gusty conditions will likely remain in place for most of the area, except for portions of central Pennsylvania and western New York. The cirrus deck that has been in place most of the day will continue to diminish over the next few hours and head off to the east as the upper level trough continues to lift out. This will allow for skies to become quite clear this evening, and with low humidity, clear skies, and diminishing winds, we will have at least marginal conditions in place for radiational cooling to take over. Temperatures will likely fall into the “cold” levels this evening as lows dip down to the upper 30’s and lower 40’s for the immediate NYC metro area. Further north and west, lows could get into the low to middle 30’s, which could cause patchy frost to develop in the areas that see the wind really calm down over the next few hours. The NWS has issued numerous Frost advisories over the Northeast, so make sure to bring in any plants that may be vulnerable to frost conditions this evening.

Tuesday will likely be another calm and cool day for the Northeast as surface high pressure begins to build in from the south and west by tomorrow afternoon. Highs will likely range from the upper 50’s to lower 60’s, with areas further north and west likely seeing readings a few degrees lower. Humidity will also remain very low tomorrow, and though this may feel like its a big deviation from the normal, but tomorrows highs will likely be right around seasonable for this time of year. The building high pressure will allow for lows tomorrow night to fall back into the low to middle 40’s tomorrow evening, and with lower overall winds patchy frost may be more likely across the area.

3km NAM showing much cooler conditions overall for the Northeast

Later This Week and Beyond

As we look ahead into the later part of the week and past the weekend, we are likely to see mid level ridging rebuilding over the east by Thursday, which should lead to a small increase in highs for a coupel of days. We should be looking at temperatures rising into the low to middle 70’s pretty much every day for the rest of the week, and then again this weekend as a second area of mid level ridging begins to build into the East by Saturday. This pattern should last us into the early to middle part of next week, before the overall pattern begins to shift largely due in part to large scale convective patterns in the tropics becoming more concentrated in this area of the globe. When this happens, we tend to see a large area of riding set up over the western United States, with a trough eventually setting up in the east. Such a scenarios would be a large departure from the normal over the past few weeks of warm and dry weather, as the eastern trough would likely bring below-average temperatures and an increased rain potential during the period. While the individual model runs seem to disagree about the exact timing of when a coherent area of troughing will set up over the east, the ensembles have been rather consistent that around the October 24th-28th period, the likelihood for this scenario is high.

Due to the level of enhanced convection over the tropics during this time as well in conjunction with leftover warm waters over the Atlantic, we may also have to keep an eye on the tropics to see if we can manage to get a late season storm out of this pattern.

We will have more on this pattern later in the week!

ECMWF Ensembles showing a deepening trough beginning to set up over the east by the middle of next week

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Have a great night!

Steve Copertino

Winds of change blowing as cooler risks set to return

October 16, 2017/1 Comment/by Miguel Pierre

Happy Monday! Much of the past several weeks have featured a similar synoptic weather headline across North America: Trough west, ridge east. This pattern had led to large scale above-normal temperature anomalies from the Plains eastward to the Mississippi River, exacerbated near the East Coast. But there are growing signs that this pattern will be changing over next few weeks.

Until now, the pattern has been largely driven by the presence of tropical forcing, from the ENSO regions where La Niña conditions have essentially taken over. We can use multiple measures and analytical approaches to understand exactly how the tropical convection is impacting global circulations, one of them being the SOI. This essentially lets us know if the atmosphere is responding in line with an El Niño, La Niña or neither.

La Nina is in the Atmosphere, but Changes are Possible

October 14, 2017/1 Comment/by Doug Simonian

After some big warmth, we finally saw some Autumn chill arrive over the past couple of days, which signifies the change of seasons. We are now approaching crunch time when it comes to compiling a winter forecast. In our Winter Forecast Webinar, one of the main topics discussed was the evolution of the La Nina and the effects it is already having on the atmospheric pattern. With La Nina conditions already having been established with regards to feedback in the atmospheric circulation, and the fact that ENSO events tend to peak in November, it would seem to be a given that La Nina would be at least somewhat or even perhaps a major driver this coming winter. And to some extent, we believe that is true. However, there is conflicting evidence regarding the future of the La Nina, and part of this will be evidenced by a pattern change to a +PNA and a trough in the East later this month. These factors will be discussed in detail in this article.

Tropical Depression Sixteen Forms Off the Coast of Nicaragua, Likely to Strengthen

October 4, 2017/1 Comment/by Steven Copertino

Good Evening!

The active hurricane season of 2017 continues on with yet another system developing, this time down near Nicaragua. Around two weeks ago, we highlighted that there was at least a moderate chance that the increased thunderstorm activity, below-average wind shear, and above normal sea surface temperatures would lead to some kind of tropical system during the first week of October. Like clockwork, we had a very large tropical wave move across the central Caribbean with an associated upper low just to its west. This greatly increased shower and thunderstorm activity over the area and began to lower pressures. Thunderstorms began to consolidate and yesterday the National Hurricane Center designated a small area of low pressure north of the Panama coast embedded in these showers and thunderstorms as Invest 90L with a high chance of development. Earlier today, surface observations and satellite data showed that the system had become sufficiently organized enough to be classified as the sixteenth tropical depression of the season with winds around 35 mph.

A little after one o’clock or so, the hurricane hunters flew into the depression to get a better idea of the systems strength and its overall structure. They did not find anything overly impressive, but they did find that the system did have a relatively well-organized center with winds around 35mph. The pressure was down to 1006mb, which is quite typical for these types of monsoonal depressions during the month of October. Since that time, the depression has not changed very much, but remains well organized with multiple curved bands and low level spiral bands present around the circulation. Convection is not all that deep at the moment, but this is to be expected during the afternoon hours with peak heating. As the sun sets and temperatures begin to cool, the temperature differential between the ocean and the cooler air aloft should spark numerous thunderstorms that should help the system begin to become better organized.

Visible satelite imagery of Tropical depression 16 just off of the Nicaraguan coast this evening with 35 mph sustained winds (RAMMB CIRA)

The depression should continue to gradually move towards the coast of Nicaragua over the next 12-24 hours, likely strengthening to a tropical storm in the process. This afternoons SHIPS text (which is a guide for intensity for cyclones) showed a rather significant chance that TD16 will rapidly intensify over the next 24-48 hours, with up to a 60% chance of the system increasing by 55 knots in the next two days. We will have to closely monitor this system over the next day or so to see how convection develops and organizes over the center. Since the system has a relatively small center already, it would not take much in the way of deep convection for the system to be able to begin to rapidly intensify over the extremely warm waters of the Caribbean and take advantage of the very strong Oceanic Heat Content below the system. History is also on the side of this system, as some of the most intense hurricane on record have intensified in the same area that this system will be tracking.

Regardless, it is likely that this system will be a moderate to strong tropical storm by the time it interacts with Nicaragua tomorrow afternoon. The system should exit central America tomorrow evening, and should be able to retain tropical storm strength as it reemerges over the Caribbean. Initially the cyclone will be over relatively shallow waters near the coast, but as it continues to accelerate north it will begin to encounter some of the warmest and deepest oceanic heat content in the world. This point will be crucial, as we will have to see if the system has a stable enough core post lander interaction. Upper level conditions will be quite favorable, with a large upper level low back away from the system off to the north and west, which should create a nice poleward outflow channel. This will allow for the system to effectively transport latent heat from the center of the storm. At this time, it seems that a strong tropical storm or minimal hurricane will be likely by Friday afternoon, when the system is nearing the Yucatan Peninsula.

Map showing the forecast points for TD16 with Oceanic Heat Content in the background. The yellow and orange values are quite high, and support a strong system.

TD16 should either pass over the Yucatan or just east by Friday evening, and eventually make its way into the Gulf of Mexico. At this point, the intensity of the storm will be highly dependent on the structure of the system, but if the system remains healthy and the core is not too disrupted from the Yucatan, then it appears quite possible that the system could enter the Gulf as a low-end Category 1 hurricane-possibly stronger if it gets its act together earlier in time. After this point, it becomes pointless to speculate on intensity once the system reaches the central Gulf by Friday, but the global models seem to indicate that there is good chance that upper level conditions will remain conducive for at least some intensification as the system approaches the Gulf Coast. TD16 should be nearing the Gulf Coast as early as Sunday morning, but the exact landfall point will likely not be known until Friday or so. For now, I would say that points from the “Big Bend” of Florida to the central Louisiana coast should keep a close on the progress of this system over the next few days as the overall intensity forecast for this system remains complicated and could change in a moments notice.

We will have an update on this system and its potential impacts for the Northeast later in the week!

This afternoons HWRF model showing TD16 steadily strengthening into a strong hurricane before landfall along the Gulf Coast

For more information and posts like this one, make sure you sign up for Premium Forecasts — where multiple detailed articles, videos, and interactives are posted each day. Also, come interact with our staff and many other weather enthusiasts at 33andrain.com!

Have a great night!

Steve Copertino

Archive for month: October, 2017