Aug 22, 2011: Stormy Pattern Continues

Notes: Today’s update includes an updated 5-Day Forecast and Tropics pages. Throughout the day tomorrow, the Tropics page will be updated, and storm summaries for last weekend’s storm and the Friday-Sunday severe weather events will be posted tomorrow and on Wednesday, respectively.

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With a trough moving into the region behind yesterday’s cold front, today brought much drier conditions into the area along with colder temperatures, peaking only in the mid to upper 70s inland, upper 70s to lower 80s in the immediate NYC area, and in the upper 70s across most of Long Island and southern CT, making today feel more like an early September day.

The area so far has seen an unusually wet August, with Central Park and JFK having seen 11.59″ and 11.94″ of rain this month, respectively. Dry conditions will continue through Wednesday, but the break from the rain will be short lived as yet another cold front brings another heavy rain risk on Thursday. Skies will clear on Friday, but trouble may be on its way as Hurricane Irene could move up the East Coast and directly affect the area, potentially shattering August rain records across the area.

Tomorrow’s Outlook:

With the trough still over the region, tomorrow will be another nice and comfortable day. With a WNW/NW wind and mostly sunny skies expected once again, high temperatures will reach the mid to upper 70s inland, upper 70s to mid 80s in the immediate NYC area, and the upper 70s to lower 80s in Long Island and southern Connecticut.

Wednesday – Friday: Storms Return Once Again

The cold air mass will slowly pull out of the region on Wednesday, bringing more of a SSW wind and warming temperatures. High temperatures will reach the upper 70s to lower 80s inland, lower to mid 80s in the immediate NYC area, and due to the south wind, Long Island and S CT will reach the mid 70s to lower 80s. Mostly sunny skies are expected as well.

By Thursday, however, the dry conditions will come to an end. Another cold front will move through the area in the afternoon and evening hours, bringing a risk of thunderstorms across the Northeast, including the area. Severe weather parameters are moderately supportive, including 30-45 knots of bulk shear and lift index down to -5. The biggest risk with these storms will once again be heavy rain, however, as precipitable water values are expected to end up near 2 inches, meaning that storms will have the potential to produce heavy rain. In addition to the heavy rain, gusty winds are also a risk with Thursday’s storms. Stay tuned for more information on these storms.

By Friday, with the cold front east of the area and another weak trough moving in, cooler conditions will return. In contrast to Thursday, when a SSW wind will bring temperatures into the mid to upper 80s from NYC and further west and upper 70s to lower 80s in Long Island/S CT, mostly sunny skies and a NNW wind will return, bringing temperatures down into the upper 70s to lower 80s across most of the area.

Saturday – Monday: Hurricane Irene Threatens East Coast

Saturday is expected to be another mostly nice day across the area, with high temperatures once again reaching the upper 70s to lower 80s across most of the area. Increasing cloud cover by the evening, however, will signal that trouble is on the way as Hurricane Irene will move up the Southeast coast and towards the Mid Atlanticc and Northeast. Yesterday’s brief post mentioned that Irene may affect the area, and the model consensus today is for the hurricane to move up the coast, directly affecting the area with heavy rain and wind.

Intensity Forecast: Since the last update, Irene has continued to move on a WNW path, and is currently just north of the Dominican Republic. As Irene will stay north of Hispaniola, no significant weakening is expected. Irene has intensified into a Category 2 hurricane earlier than expected, and with a mostly favorable environment ahead of it with high SSTs and low wind shear, additional intensification is expected, and Irene will likely become a Category 3 hurricane by at least Tuesday morning, if not the afternoon. With a mostly favorable environment persisting and the potential for Irene to rapidly intensify, I updated the forecast to show Irene strengthening into a lower to middle end Category 4 hurricane, peaking with 140-150 mph sustained winds.

Track Forecast: Irene’s track is mostly certain for the next day, moving on a WNW track and staying just north of Hispaniola. By Wednesday and Thursday, however, there is increasing uncertainty with Irene’s track. Looking at the latest models, the UKMET, NAM and GFDL are the western solutions, with Irene moving through Florida, likely moving up the coast in the form of remnants. The ECMWF and GFS are in the middle, with Irene moving right up the coast, affecting the coast from the Carolinas to NYC and New England with heavy rain and strong winds. The GGEM is further east with the storm staying mostly offshore, but is an outlier with how it handles the storm, especially due to the timing being off by at least a full 24 hours compared to the other models.

Looking at the latest trends, the models have shifted slightly east, shifting from a consensus for the storm to track just east of Florida as of this morning to a South/North Carolina landfall as of this evening’s runs. Last night’s westernmost solutions, showing a track in the Gulf of Mexico, have shifted east as well. There is still uncertainty for this time period, but at this time, I expect Irene to start recurving earlier than the western models show, keeping Irene mostly east of Florida with a landfall somewhere from the northern coast of South Carolina to east central North Carolina. Irene would then follow a path not too far off the coast as it moves towards the NNE/NE and becomes extra-tropical, staying just east of Long Island and over Cape Cod. Such a solution would affect the area with rain and wind, but keep the worst of Irene to the east of NYC. Confidence on this solution is not very high, and Irene could end up anywhere from a track just west of NYC, to a track just east of NYC, to a track mostly offshore with minimal impact in NYC. Stay tuned for more information on Irene over the next few days.

Impact On East Coast/NYC: As previously mentioned, there is still uncertainty with Irene’s exact location, but Irene will affect the area, whether directly or indirectly. Should Irene take the track I previously mentioned, the area would be affected by a strong Tropical Storm Irene on Sunday through Sunday night. NYC would see rain and wind, but the heaviest rain would stay in Connecticut and Long Island. This is a more eastern scenario, and should Irene take the middle path as suggested by the GFS and ECMWF, which is a reasonable solution that cannot be ruled out, the area could experience heavy rain, potentially well over 4 inches, and up to near hurricane force wind gusts. It is also a possibility that Irene tracks just west of NYC in the form of remnants, which would bring moderate to heavy rain into the area but with lighter winds.

There is still a lot of uncertainty with Irene, and the forecast could change towards more or less impact, but Irene is expected to affect the area, whether it’s directly or indirectly. Stay tuned for more updates on Irene in the Tropics page, where updates will be posted 2-3 times a day, and with the daily evening discussions, which will discuss Irene’s impact on the area in more details.

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