Brief Thunderstorm Update: Behind today’s line of storms, which dumped a general 1/4 to 3/4 inch of rain from NYC and further west and less than 1/4 of an inch in Long Island and southern Connecticut, conditions have dried up. The actual cold front is approaching the area, but will only bring isolated thunderstorms to the western parts of the area before drying out. The immediate NYC area and Long Island/S CT are expected to stay dry through tonight.
Hurricane Irene: Western Long Island Landfall Possible
Over the last day, uncertainty continued with Hurricane Irene’s track in the area as the computer models showed solutions ranging from Irene staying east of Long Island to a scenario where its remnants move through central Pennsylvania. These uncertainties will continue through at least tomorrow afternoon/evening, when a much clearer image should emerge on Irene’s path, but at this time, there is already a better idea on where Irene could make landfall, and at this time, it appears that this could be in western Long Island or potentially over NYC itself.
Irene’s Intensity: After last night’s eyewall replacement cycle, Irene improved in organization throughout the day. Irene has developed a more organized eye this afternoon and evening, and since the last update, its minimum pressure dropped to as low as 946 mb, its lowest pressure so far, and the equivalent of approximately a weak category 4 hurricane. Despite the pressure drop, sustained winds have failed to increase, and actually are below 115 mph in most of the hurricane. We have seen a scenario like this happen with Hurricane Ike in 2008, where the pressure dropped but the winds failed to increase, and as a result, Ike increased in size. The same may happen with Irene, and Irene will remain a very large hurricane as it begins to move up the East Coast.
There is an area of higher wind shear to the north of Irene, however there are warm sea surface temperatures as well, in the mid 80s. With signs of Irene already starting to intensify, additional intensification is expected, and Irene will peak with sustained winds between 120-125 mph during the day tomorrow. As Irene reaches North Carolina where there will be colder sea surface temperatures, Irene will begin to weaken, but especially due to its large size, only slow weakening of Irene is expected, and it will weaken to a category 2 hurricane on Saturday as it makes landfall in eastern North Carolina. From there, Irene will gradually weaken as it moves up the coast, and is expected to be a weak category 1 hurricane with 75-85 mph sustained winds as it makes landfall somewhere from eastern Long Island to NYC.
Irene’s Track: As with the last few days, the most difficult part of forecasting Irene is its track. While the range in model solutions has slightly decreased since yesterday, the models continued to shift back and forth, going from an eastern Long Island track yesterday to a western New Jersey track this afternoon and back to a NYC track this evening. The ECMWF and GFDL models were the main models yesterday to show a far inland track through Pennsylvania, but the other models have not shifted towards showing such a track, and the main model consensus takes Irene over western Long Island or NYC. There are still another 72 hours until Irene makes landfall in the area, and some changes in the track are still possible, but model differences will only decrease from this point and on, and a better model consensus is expected to develop starting at least tomorrow afternoon/evening, when Irene will be two days away from making landfall.
For the short term, Irene will continue to move towards the NNW, and will switch to a north direction tonight or by tomorrow morning. From there, Irene will begin to turn more towards the NNE as it makes landfall in eastern North Carolina. From there, the question is what direction Irene takes, as it could go north/NNE and hug the coast, making landfall in NYC, or Irene could take more of a NNE/NE direction, making landfall in central or potentially eastern Long Island. A few models continue to portray a scenario where Irene moves due north and enters eastern Pennsylvania, however this solution is becoming much less likely, especially as the model which showed this solution with the majority of its runs, the ECMWF model, has shifted to the east. The latest models continue to shift back east; in fact, the latest 00z NAM run shows Irene making landfall in eastern Long Island, sparing NYC from the worst of the hurricane.
For tonight’s update, my forecast track shows little change from yesterday’s forecast, showing Irene moving NNE from North Carolina, just east of the New Jersey coast, before making landfall in central Long Island. This track is not final yet, however, and it is possible that Irene could shift west towards a NYC landfall, or Irene could shift even more east once again, with landfall in eastern Long Island, and the scenario where Irene’s center stays east of Long Island still cannot be ruled out, although it is a less likely scenario. It is a possibility that should the models continue to trend east with increasing support for such a solution, I may shift my forecast track towards an eastern Long Island landfall, but otherwise I am sticking with a central Long Island landfall at this time. Stay tuned for more information on Irene’s track with updates in the Tropics page tomorrow, the first one at 11 AM.
Irene’s US/NYC Impact: Irene will be a large hurricane when it reaches the area, and even if it stays east of NYC, its impacts will still be felt all the way to western NJ and eastern Pennsylvania. As previously mentioned, there is still uncertainty with Irene’s track, and it is possible that Irene could shift further west or east. Shifting Irene further east would take the worst of Irene’s rain and wind further east, but due to its large size, heavy rain and strong wind gusts will still be felt all the way to the immediate NYC area. With Irene still a category 1 hurricane when making landfall in Long Island, sustained winds of up to 75 mph are possible in Long Island during landfall, with destructive wind gusts gusts up to 90 mph possible. A track near NYC will bring 80+ mph gusts into parts of the city itself as well as the immediate NYC area, while an eastern Long Island track will shift these gusts into Long Island, with wind gusts up to at least 60-70 mph in NYC.
Forecast For NYC Area: Irene’s outer bands are expected to arrive by Saturday afternoon, with cloudy skies and scattered thunderstorms which could produce heavy rainfall. Saturday afternoon and evening will still be relatively calm, but winds will begin to increase overnight into the late morning as steady rain and thunder begins to move in from the south.
The worst of Irene will take place during the day on Sunday. Based on my latest forecast, Irene’s heaviest rains will be in western Long Island into NYC, where anywhere from 6 to as much as 10-12 inches of rain could fall. Irene’s strongest winds would cover Long Island and southern Connecticut, with sustained winds up to 60-70 mph possible with wind gusts potentially between 70-90 mph. In the immediate NYC area, the rain will be the biggest issue, with 5 to 8-10 inches of rain expected. Gusts will be less than those in Long Island, with sustained winds between 50-60 mph possible along with gusts potentially between 60-75 mph. Should Irene track closer to NYC than currently expected, these gusts will be higher. In the western parts of the area, moderate to heavy rain is expected with a total of 2 to 6 inches possible. Winds will be lighter, with gusts between 40 and 50 mph expected.
Rain and wind will gradually increase in the morning, with the worst of Irene in the mid afternoon hours as its center makes landfall in Long Island. After at least 8-10 PM, conditions across the area will begin to calm down, with decreasing winds and rain tapering off. Clearing skies are expected for the late overnight hours, with mostly sunny skies returning for Monday.