As of 3AM, Hurricane Irene’s top winds are down slightly to 90 MPH as it moves NNE along the North Carolina Coast.
What is hurting Irene? She felt some southwesterly wind sheer from a trough of low pressure over the Gulf of Mexico during the past 24 hours, but has now gotten beyond that. The circulation being partly over land interrupts the even inflow to the storm. Some dry air has also worked into the western part of the circulation, making it look irregular.
What will aid Irene? The center of the hurricane should remain mostly over water as it moves away from NC later Saturday. The water temperatures are quite warm right up to Long Island NY.
When is storm for the Boston area? Although tropical showers are possible today, the heaviest tropical rain will occur tonight and Sunday morning, and the strongest wind will occur Sunday afternoon and evening.
Tornadoes? As noted in the previous blog post, tropical cyclones can and do produce tornadoes when they come over land. This takes place because friction encountered by the storm over land lowers the wind speed there, while the winds just above remain stronger. This results in wind sheer, which can be explained as differences in wind speed and direction as you go from the ground up. These differences create the rotation that becomes tornadoes. These are usually embedded in some of the rain bands on the right front quadrant of the storm, or in this case, to the northeast of where the center is. Hurricane-produced tornadoes are weaker than their severe thunderstorm cousins, but can cause significant damage. Do not be surprised if a tornado watch is issued for at least the eastern half of MA including RI and southern NH by the National Weather Service on Sunday.
Where is the center of Irene going? I believe Long Island landfall will take place slightly earlier than I said on the previous post, by 6PM Sunday at the latest. I’m edging my forecast track east very slightly, based on the fact that the hurricane had already turned to the north northeast as of late Friday night and is not expected to turn back to north, but continue north northeast. The center will probably cross central Connecticut and Massachusetts, passing over or just west of Worcester by 8PM. One change in my thinking from earlier is that the air mass will be very tropical and with water temperatures quite warm right up to long island, it may take a little longer for Irene to start losing tropical characteristics. Once it gets into northern New England later Sunday night, it will start to transition into a regular storm, at which time the winds around the storm, though weakening, may expand and cover a larger area. How rapidly this takes place will determine how much wind lingers over southern New England after the storm leaves. Keep in mind that strong and gusty winds may continue into Monday, even though the storm will be long gone by then.
Wind? East of the center, expect tropical storm-force winds (39-73 MPH)with the potential for hurricane-force gusts (74 MPH or higher), strongest near the coast and over higher elevations. Winds will blow mostly from the south southeast to south in the big wind regions. West of the center, winds will be mostly east to northeast as the storm approaches, shifting to north and northwest as it passes, and may be strong and gusty at times, with possibly the strongest winds coming as the storm is departing Sunday night.
Rain? Tropical showers and possible thunderstorms, with some heavy rain bands, will result in around 1 to as much as 3 inches of rain in eastern areas, east of the center. Amounts will be much heavier to the west of the center, with 4 to 7 inches of rain common. Amounts of over 7 inches may occur in some up-sloping wind regions in western Massachusetts and then up into portions of northern New England.
Coastal storm surge & flooding? East-facing coastal areas will see splashover and flooding especially at high tide, but should not be any worse than during powerful winter storms. South-facing areas, especially the bays of the South Coast, will see storm surge flooding as high as 4 to 8 feet. Significant flooding is likely in these areas.
I hope this breakdown of the storm covers just about everything. If you have any questions, do not hesitate to post them in the comments section below.
Beyond Irene? Well it looks like a great stretch of weather follows this storm for the first half of next week!
Updated Boston Area Forecast…
TODAY: Mostly cloudy to partly sunny, warm, and very humid. Isolated showers in the morning. Scattered showers in the afternoon, a few of which may be heavy. High 73-78. Wind S to SE 5-15 MPH.
TONIGHT: Cloudy. Episodes of tropical showers, heavy at times. Chance of thunderstorms. Areas of fog, possibly dense at times. Low 64-69. Wind SE to S 5-15 MPH.
SUNDAY: Overcast. Fog possible in the morning. Tropical showers most numerous in the morning, likely heavy at times with a chance of thunderstorms as well. Showers may become less numerous for a time in the afternoon, but a core of heavier rain is expected later in the afternoon. Mild with tropical humidity. High 70-75. Wind SE to S 15-25 MPH increasing to 25-45 MPH with gusts 50 MPH or higher becoming quite common, possibly up to 75 MPH or slightly higher over coastal and higher elevations by late in the day. Isolated tornadoes are possible, but not likely.
SUNDAY NIGHT: Rain and showers ending from south to north with breaking clouds following. Still mild and very humid. Low 65-70. Wind SW to W 15-35 MPH with gusts 45-55 MPH.
MONDAY: Mostly sunny. Warm and humid. High 80-85. Wind W 15-30 MPH and gusty, diminishing slowly.
TUESDAY: Sunny. Low 58. High 79.
WEDNESDAY: Sunny. Low 56. High 78.
THURSDAY: Mostly sunny. Low 62. High 83.
FRIDAY: Partly sunny. Low 63. High 82.