Aug 23, 2011: Hurricane Irene Discussion

Note: A poll has been opened for Irene’s impact in NYC. Please vote your thoughts in the poll, which will close on Saturday afternoon.

With a chilly air mass sticking over the region, today was another mostly sunny day across the area with below average temperatures, peaking in the upper 70s inland, upper 70s to lower 80s in the immediate NYC area, and in the mid to upper 70s in Long Island and southern Connecticut. Temperatures will slowly warm up tomorrow and again on Thursday as a cold front moves through the area, potentially bringing a squall line late in the day containing heavy rain. This is just a taste of what will come in the weekend, as Hurricane Irene threatens to bring over 8 inches of rain and strong winds to parts of the area, especially in Long Island and Connecticut, on Sunday.

Wednesday – Friday Outlook:

Tomorrow will be another nice day but with slightly warmer temperatures due to a SSW wind, reaching the upper 70s to mid 80s from NYC and further west and the mid 70s to lower 80s in Long Island/S CT. On Thursday, a cold front will move through the region, which combined with high precipitable water values and decent severe weather parameters, could result in a squall line moving through the area in the late afternoon/evening hours, producing heavy rain locally up to 1-2 inches and gusty winds. More information on Thursday’s storms, including a forecast map, will be posted with tomorrow’s update. Friday will bring drier and colder conditions, with temperatures and cloud cover similar to those of today.

Hurricane Irene Update: Long Island/New England Targeted

Since yesterday, the forecast models have continued to change Irene’s track in the region, and a more solid consensus is growing for Irene to stay near or just east of Cape Hatteras, moving NNE from there and ending up just east of Long Island. Such a scenario would bring the worst of Irene into Long Island and New England. Despite this, there is still some uncertainty, and it is still possible that Irene could either shift east, sparing most of the region, or shift west, putting NYC directly in Irene’s heaviest rain area.

Intensity Forecast: Irene has unexpectedly weakened over the last few hours, and is now a Category 1 hurricane. Despite this, Irene’s pressure has been consistently dropping and is now down to 969 mb, the equivalent of approximately a strong Category 2 hurricane, and Irene has reorganized itself with a more visible eye. As a result, I am expecting Irene to re-intensify into a Category 2 hurricane tonight, perhaps as soon NHC’s 11 PM update. Irene will continue to intensify and is expected to reach Category 3 intensity later tomorrow or on Thursday at the latest, and while less likely, a weak Category 4 hurricane cannot be ruled out. Should Irene’s current intensification continue, it is not out of the possibilities that Irene becomes a Category 3 hurricane as soon as 11 AM tomorrow. As Irene reaches the cooler waters north of Cape Hatteras and starts to become extra-tropical, Irene will weaken around Saturday to a Category 2 hurricane, then a category 1 hurricane overnight.

Track Forecast: As with yesterday’s update, Irene’s forecast track remains the biggest challenge in the forecast, and any small shift could either keep the worst of Irene offshore or could hit New Jersey, NYC and the rest of the tri-state area with very heavy rain and strong winds. For the short term, Irene will continue to move WNW tonight, changing more towards a NW direction tomorrow. By the time that Irene reaches northern Florida’s latitude, approximately where it should begin to turn more north and slightly NNE, Irene is expected to be south of eastern North Carolina, and will begin to move NNE from that point. There is some uncertainty regarding whether Irene makes landfall near Cape Hatteras or stays just offshore, and at this time, there is an equal chance of both happening. For tonight’s map, I put Irene just east of Cape Hatteras, but it is possible that Irene shifts slightly west and makes landfall there.

From North Carolina and further north, uncertainty increases on the track. A trough is expected to approach the Northeast from Canada on Saturday/Sunday, with Irene catching up to that trough and accelerating to the NNE/NE while becoming extra-tropical. There is some uncertainty with Irene’s interaction with the trough, and as a result, there are two main scenarios at this time. In the first case scenario, Irene will continue to move NNE from Cape Hatteras, making landfall near central Long Island. This scenario would bring very heavy rain and strong winds to New Jersey, NYC and SE NY, with slightly less rain but much stronger winds in Long Island and southern Connecticut. The second scenario is where Irene recurves more to the NE, which would take it just east of Long Island with landfall near Rhode Island or Cape Cod. At this time, the model consensus is pointing towards the second scenario, but the first scenario cannot be ruled out as well, and it is possible that I may shift my forecast track slightly west with tomorrow’s update if the model consensus shifts further west and becomes more concentrated with a smaller spread. Stay tuned for more information on Irene with the next update in the Tropics page at 11 AM Wednesday.

Irene’s US/NYC Impact: With the two scenarios previously mentioned, there is still uncertainty with Irene’s exact impact, but at this time, Long Island and southern Connecticut are the most likely places to see the worst of Irene out of the tri-state area. Irene will start to affect the area on Saturday night with developing rain and increasing winds, and the worst of Irene will take place throughout the day on Sunday before calming down overnight. The places that will see the worst of Irene, currently in the Likely Impact Zone but could be further east or west, could end up with 5 to as much as 12 inches of rain resulting in significant flooding, especially when combined with the rain so far this month and Thursday’s storms, along with potentially near hurricane force wind gusts (74 mph). Places further west will see lighter rain, up to 5 inches, with lighter wind gusts, in the tropical storm force range (40-74 mph). There is still uncertainty with Irene’s impact, but Irene has the potential to be a dangerous storm which could result in significant damage across the East Coast. Stay tuned for more information on Irene over the next several days.

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