Thomas is an avid weather enthusiast, landscaper and organic gardener. This blog is dedicated to Northeast and tropical weather forecasting. Enjoy!
By: sullivanweather , 3:06 PM GMT on August 25, 2011
Current watches, warnings and advisories.
Current watches, warning and advisories issued by the National Weather Service. Courtesy of NOAA.
Your Northeast Forecast
All eyes are on Irene this morning as it churns over the Bahamas as a category three major hurricane. This storm has the Northeast in its crosshairs this weekend, promising to bring flooding rainfall, damaging winds and high storm surges along the coast. Before Irene's arrival there will be a couple of systems to deal with; the first today in the form of a fairly decent cold front bringing the chance for isolated severe thunderstorms and heavy rainfall and the next on Saturday as another possible area of heavy rainfall indirectly associated with Irene moves up along the coastal plain. As Irene chugs into Canada early Monday morning a much cooler and drier airmass will filter in and last till Wednesday, giving the region a chance to clean up and dry out.
A sharp trough and its associated cold front will slide across the Northeast today, shearing out in the process as it meets up against a strong offshore deep-layer ridge of high pressure. This is the same ridge responsible for steering Hurricane Irene towards the East Coast. Out ahead of this front deep moisture is streaming northward on a brisk 30-35kt low-level jet, pumping precipitable water values around the 2" range, so it's a rather humid start to the day for much of the region. Also streaming northward ahead of the front along a pre-frontal trough is an area of widespread showers and embedded thunderstorms moving through central Pennsylvania and New York. Rainfall with these storms have been heavy this morning, with some places picking up over an inch of rain. This area of precipitation will gradually shift eastward as the day progresses, reaching eastern New York and Western New England around lunchtime and slowing considerably thereafter. Visible satellite imagery shows extensive cloud cover over much of the region save the immediate coast, so insolation will not be too big a role in heating things up in this humid airmass. This should limit the severe weather threat but it will still be present. Instability should easily reach 1,000J/kg along the coastal plain, yielding plenty of energy for convection. As the pre-frontal trough moves towards the coast expect a new round of storms to fire up this afternoon from southeastern Pennsylvania to southern New England while further west along the actual cold front, more scattered convection and maybe a forced narrow line of storms will continue to fire until it passes by So another round may be in store for areas of central Pennsylvania to the Finger Lakes region. Further to the north over central/northern New England cloud cover will keep surface instability low but it will be made of aloft as a strong push of positive vorticity moves trough associated with the mid-level disturbance, providing the extra lift needed for scattered showers and thunderstorms here as well. The front will have a bit more progression the further north one heads so rainfall won't be nearly as heavy across the North Country. However, along the coast as the flow aloft aligns to the front expect this feature to slow down and stall, providing an ideal set-up for training thunderstorms and flash flooding given the wet antecedent conditions. Rainfall amounts should range from a quarter to three quarters of an inch to the north with a half into to an inch and a half to the south with possibly higher amounts in training thunderstorms. High temperatures will be in the 70's for most areas today, though some upper 60's are possible given the quicker onset of thicker clouds over the higher elevations of the North Country while sections of extreme southern New Jersey, where some breaks of sun occurred this morning, temperatures might climb into the low 80's. It will be quite muggy in all areas except for the far northwestern portion of the region where the cold front has passed.
The front reaches just offshore and stalls out tonight as showers and thunderstorms taper off in the evening hours. Otherwise expect partly to mostly cloudy skies and a slow drying of the airmass across the northern third of the region. To the south it will remain muggy with low temperatures in the mid 60's to low 70's. To the north, mid 50's to low 60's should do.
On Friday the humidity begins to creep back north as the front along the coast washes out. There will be more sun than clouds, especially over the interior, but overall a very nice day. There's an outside chance for an isolated shower across southern New Jersey where moisture will be a bit deeper but that's it. A great day to make preparations for the arrival of Irene this weekend. Temperatures will run a few degrees above normal with highs reaching into the mid to upper 70's across the north with low to mid 80's south.
It's the calm before the storm Friday night as Irene will be approaching the Outer Banks of North Carolina at this time from the south. Over the Northeast, 500-700 miles north of the storm, signs are there may be a predecessor rainfall event developing over New Jersey, southeastern New York and southwestern Connecticut. Should this occur there will be some very intense rainfall associated with very slow-moving thunderstorms which may cause localized flash flooding concerns. Elsewhere expect mainly partly cloudy skies and temperatures on the mild side, running 5-10 degrees above normal.
As the weekend begins there will be a steady deterioration of the weather from south to north in most areas east of the I-81 corridor. For those west of this region the forecast is fairly straight forward. Expect a veil of high cloudiness to move over the region on Saturday, sticking around all weekend. In the far west these high clouds will be thin, allowing for a greater diurnal swing in temperatures from the upper 70's during the day to the mid 50's at night. The clouds will thicken the further east one heads, knocking a few degrees off daytime high and keeping overnight lows a few degrees warmer. Cloud cover will begin to diminish Sunday night as a dry, brisk westerly breeze develops in the wake of Irene.
For areas along and east of I-81 it will be a harrowing weekend. Pre-event will be ongoing during the early morning hours on Saturday for areas along the coastal plain up to Connecticut. Rainfall associated with the pre-event will generally range from a quarter to a half inch but localized areas which see training storms could easily pick up three inches or more. Keep in mind this will be the one last day to complete preparations for Irene. High clouds will be on the increase throughout the day, lowering and thickening across areas to the south by the afternoon. Cape May, County, New Jersey may even begin to see the first outer bands of Irene move in before dusk. Winds will begin to increase out of the east, beginning the day in the 10-15mph range along the coast (5-10 inland) and increasing to 15-25mph along the coast by evening (10-15 inland).
By Saturday night Irene will be starting to make her presence felt as the outer rainbands begin to spread over the coastal plain of New Jersey and back across southeastern Pennsylvania during the evening hours. By this time Irene should be passing the mouth of the Chesapeake, pounding the Tidewater region with hurricane conditions. Irene will also begin to accelerate north at this time as she becomes embedded within the mid-latitude flow. This will allow for a quicker northward expansion of precipitation after midnight, reaching Long Island, extreme southern New England, southeast New York and eastern Pennsylvania before daybreak. Further north expect just a continuation of increasing cloudiness ahead of Irene. Temperatures will be quite warm as the tropical airmass moves over the region with most places across the interior remaining in the mid 60's while areas along the coast remain in the low 70's.
Sunday will be a day many youngsters will one day tell their grandkids about. Hurricane Irene will begin the day about 25 miles off the coast of Chincoteague, Virginia, heading just east of due north for western Long Island. The model guidance for Irene's track has come into much better agreement with clustering over the western portion of Long Island as the storm gets captured by a strong southerly flow between a very powerful deep-layer ridge over the western Atlantic Ocean and a digging shortwave trough over the Great Lakes. On this track Irene promises to bring hurricane conditions for a huge section of real estate as the storm hugs the Jersey shore then slams ashore Long Island by the evening hours. Irene's impact will be felt far and wide and will be detailed here and in the tropical section of the blog. Temperatures will remain in the 70's for most areas with upper 60's over the higher terrain.
Due to Irene's expected girth as the storm moves north along the coast it is unimportant to pay attention to where the center comes ashore in this situation as her effects will be felt far and wide. Irene will have a strong massive wind field that will bring hurricane force wind speeds for most of the coastline from Cape May to Cape Cod. For inland locations, hurricane force winds will be felt in areas up to 40 miles east of the center and 25 miles west of the center until the storm spins down to a tropical storm up to 150 miles inland over New England. Additionally, just about all of New England, eastern New York, New Jersey and eastern Pennsylvania will see at least tropical storm force winds sustained or in gusts, depending on how far one is from the center. The stronger winds will be felt on the east semi-circle of the storm. Higher elevations over 2000' will also see hurricane force wind gusts due to the circulation remaining strong aloft. Highly populated cities susceptible to seeing hurricane force winds include New York City (especially the boroughs of Queens and Brooklyn);Atlantic City, New Jersey; Hartford, Connecticut; Springfield, Massachusetts and Providence, Rhode Island. Once again, due to Irene's large and well-developed circulation the potential wind impact from Irene will be maximized. Unlike smaller, less-developed tropical systems where the wind field is sporadic and concentrated to localized areas, Irene's will be much more widespread and take much longer to dissipate. This means bad news for areas across the interior as much of this area has been in a wet pattern this month, leaving soils saturated and trees vulnerable to be toppled by the wind.
Despite how severe of a wind event Irene will bring to the coast, perhaps the biggest impact from Irene will be the excessive rainfall and inland flooding. As mentioned, the antecedent conditions are extremely wet. Some areas are already approaching their record wettest August and these includes stations around since 1955, when two tropical systems affected the Northeast. The frontal system will bring up to an inch of rainfall today and the pre-event has the potential to bring much more all before the arrival of Irene. Irene will be non-typical of a Northeast hurricane caught in the mid-latitude flow as it won't be zooming through the region as most of these storms do. Instead it will make a steady progression through the Northeast around 15-20 mph; fairly quickly, but relative to a Northeast hurricane, a graceful stroll. Thus, Irene will be capable of producing extremely heavy rainfall amounts.
Now that it appears Irene will track just east of due north after passing the Carolinas, the hurricane will take a more western track than anticipated yesterday. This will expand the rain coverage much further west than anticipated yesterday. As the storm interacts with land much of the convergence will occur on the west side of the hurricane due to the frictional component of the land as opposed to the eastern side of the storm, which will be over the water. This increasing angular momentum within the storm will cause Irene to become lopsided, with most of the heaviest rainfall occurring on the western semi-circle of the storm. Not an odd occurrence but certainly bad news for the Northeast as it spreads out Irene's wrath, with flooding rainfall west and stronger winds east. Rainfall amounts will range from 6-10"+ for areas up to 100 miles west of the track of the center with amounts quickly tapering west of there. Along the track of Irene and for areas up to 25 miles east of the track of the center 4-8" of rainfall will be common. For the remainder of New England rainfall amounts should range from 2.5-5". In all areas these amounts are enough to bring just about every waterway out of their banks; creeks, streams and main stem rivers. Should there be excessive rainfall with the pre-event prior to Irene flooding of historic proportions are possible across areas of northern New Jersey, northeastern Pennsylvania, southeastern New York and Connecticut.
While it is too early for specific area storm surge forecasts due to track of Irene, timing of high tide, etc., a general picture is emerging for what we can expect to see from Irene's storm surge. For areas where the center comes ashore and up to 50 miles east expect a storm surge of at least 6-10' above expected tides. Some of the narrow bays may even see tides up to 15' above expected tides, which would be of historic proportions. Should a landfall occur on Long Island even areas east of the maximum zone of storm surge as far east as Cape Cod will see storm surges of 4-8' above expected tides. Areas further up the New England Coast should see a 2-4' storm surge. Along the New Jersey Coast storm surge of 3-5' is expected but should the storm take an inland track (a slight possibility) this could easily be doubled. It must be repeated that these are extremely preliminary estimates, however, residents along the South Shore of Long Island should seriously consider evacuations now as they are right in the bullseye.
After the passage of Irene much cooler air will enter the Northeast as a mainly dry trough digs into the region. Across the North Country, Irene, undergoing extra-tropical transition, will provide lingering heavy rainfall in the morning, tapering to upslope showers by afternoon. Elsewhere skies will gradually clear and winds will be brisk out of the northwest. High's will range from the 50's across the north to the 70's south. Seasonable weather continues Tuesday and Wednesday with mainly dry weather. Heights build to close out the week as temperatures climb back above normal with continued mainly dry conditions.
IR Satellite image of Hurricane Irene.
Radar: Northeast Region Loop
Radar loop of the Northeast region. Courtesy of Weather Underground.
Sea-surface temperatures off the Northeast Coast. Courtesy of NOAA.
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