Hurricane Dorian’s center passes well southeast of the city to start the weekend. Because of its large and expanding size, it will still influence our weather. Once Dorian passes, we’ll see improving conditions though cooler temperatures will be the rule with Canadian high pressure taking over.
Rest of today – mostly cloudy with isolated showers, more likely during the late afternoon and evening hours. It’s difficult to say even now whether the outermost rain bands from Dorian actually manage to hit the city, and even if they do, it’s also unclear how intense they will be. High temperatures in the low-70s. Overnight lows in the low-60s with cool, northeasterly onshore flow due to the cyclonic circulation around Dorian. For more info, see this detailed forecast.
GOES satellite imagery of Hurricane Dorian
Saturday – much improved conditions as drier air works in behind Dorian. Mostly sunny with high temperatures in the upper-70s. Overnight lows in the low-60s.
Sunday – a touch cooler though still mostly sunny with high temperatures in the mid-70s as winds turn more to the north and Canadian high pressure builds. Overnight lows in the low-60s.
Weather Prediction Center surface forecast for 8AM Sunday
Monday – high temperatures continue a 5-6°F below average trend, with highs forecast to be in the low-70s and mostly sunny skies. It will definitely feel like fall. Overnight lows in the mid-60s.
The forecast for tomorrow in NYC hinges largely on what happens with Hurricane Dorian’s track. Although the center of this still powerful storm is expected to pass well south of the region, its influence on wind patterns, and its outer bands of clouds and rain could still impact the city. In essence, as has been alluded to by others, Dorian’s impact on NYC will be not unlike that of a Nor’easter. This forecast, as a result, carries a fair deal of bust potential especially as it relates to precipitation totals and to some extent with the maximum sustained winds.
My Forecast High: 71°F | Low: 63°F | Max sustained winds: 24 mph | Total precipitation: 0.02″ – verification will come from METAR data for the period between 2AM Friday and 2AM Saturday (06Z Friday to 06Z Saturday) at LGA (LaGuardia Airport), and the KLGA Daily Climate Report.
Verification High: 69°F | Low: 60°F | Max sustained winds: 32 mph | Total precipitation: 0.03″ Surprisingly, despite personally witnessing some moderate rain bands move over Midtown on Friday, KLGA itself only picked up 0.03″ of precipitation from the outer rain bands of Dorian that hit the city. That means my precipitation forecast was almost spot-on in this respect. I was 2-3°F too warm on both high and low temperatures. Statistical models weren’t really expecting much in the way of rain. When rain did occur temperatures cooled somewhat via evaporational cooling since the atmosphere did start off on the dry side Friday and there was room for this cooling to take place. The forecast bust, as it turns out, was with the maximum sustained wind, where I fell short by 8 mph. Despite low rainfall totals, even a small bout of rain could have kicked up winds via downward momentum transfer of somewhat faster moving winds aloft. The other thing to remember is that northeast winds are climatologically most likely to produce the fastest winds in September. This wind direction also happens to have a long fetch over open water for many north-facing shores in NYC, including KLGA. That long fetch over open water would tend to reduce surface friction since water is smoother than land on average, and allow for faster winds.
Weather Prediction Center surface forecast for 2AM Friday at the beginning of the forecast period
Weather Prediction Center surface forecast for 8PM Friday
Current GOES satellite image of Hurricane Dorian – it’s cirrus shield has already reached NYC
Synoptic Set Up Hurricane Dorian will be approaching from the south and the storm’s center will accelerate northeast well offshore of the NYC area during the forecast period. At the surface, high pressure will be in place early in the forecast period, but will weaken quickly. A surface trough is forecast to form and travel east while a second surface trough associated with Dorian may form late in the forecast period.
At the 500 mb level, a shortwave trough will be moving east. This will assist in continuing to accelerate Dorian off to the northeast. This interaction with Dorian will also bring some relatively strong divergence across the area later in the day, providing some enhanced lift that could be conducive to rain. Finally, at the 300 mb level, there is some evidence that we could be in a favorable exit region of a jet streak. This will server to further enhance upper level divergence and lift at these levels.
North American Model (NAM) forecast for 500 mb height and vorticity at 11PM Friday. The intense vorticity associated with Dorian is clearly evident in the bottom right, along with a fairly potent shortwave trough approaching from the west
High Temperatures GFS, NAM, and NBM are in consensus that Friday will be a much below average day in terms of high temperatures. All three statistical models come in at 71ºF or 72ºF for high temperatures, which is about 8-9ºF below normal for this time of year. The synoptic setup for tomorrow favors northeasterly to east-northeasterly winds given the counter-clockwise flow around Dorian’s center, and similar to the situation with a passing Nor’easter. These wind directions favor onshore flow, bringing in a cooler, moist air mass off the Atlantic into the area. With sea surface temperatures hovering right around 70ºF, there’s not too much more room for cooler temperatures. This set up also favors low clouds, and this is indicated in the statistical models as well. I don’t see too many “gotchas” so I’m going with 71ºF.
Low Temperatures Statistical models show the chance that the low temperature during this forecast period may actually occur overnight going into Saturday. The fact that GFS, NAM and NBM all converge on 63ºF as the low gives me increased confidence that this is a fine temperature to settle with. There aren’t any signs of strong temperature advection or changes in airmass to warrant a big deviation from this.
NAM MOS forecast
GFS MOS forecast
Max Sustained Winds Even though the center of Dorian will pass well offshore of NYC, the large radius of its wind field will still result in fairly robust winds across the area. The average of GFS and NAM MOS is about 18 knots. Climatologically speaking, northeasterly winds are actually the most likely to produce winds exceeding 21 knots during September. I think it’s possible that if a rain storm related to Dorian moves through, we could see sustained winds up to about 25 mph with some downward momentum transfer possible.
Total Precipitation This is a tricky precipitation forecast because forecast models like SREF place the probability for precipitation over 0.10″ not that far away from the city, and the gradient of probabilities increases quickly the further east you go. This makes sense, since the best conditions for rainfall will be closer to the core of Dorian. Given that the track forecast for Dorian seems to be shifting further offshore, though, it doesn’t make sense to bank on a big rainfall total from this event. The GEFS and SREF QPF plumes average is only 0.06″, hardly a big rainfall total, though the spread is anywhere from nothing to about 0.20″. The atmosphere starts of relatively dry tomorrow, and 850 mb forecasts don’t suggest any low-level jet conveying deep moisture (though Dorian can definitely provide this too). Furthermore, forecast soundings show a pretty persistent dry layer in the mid-levels of the atmosphere. So despite the fact there’s going to be some enhanced lift from divergence at the 500 mb and 300 mb levels tomorrow, I’m erring on the side of this passing storm only dealing a glancing blow. I don’t think it’ll be completely dry, though, like GFS and NAM MOS, so I’ve gone ahead with 0.02″ as a forecast for total rainfall.
NAM forecast for 850 mb relative humidity and winds at 11PM Fridayat
GFS forecast for 850 mb relative humidity and winds at 11PM Fridayat
During my time taking classes as part of Penn State University’s Undergraduate Certificate in Weather Forecasting, we were taught that understanding the climatology of the location you are interested in is an important prerequisite for making accurate forecasts. This post continues on this theme, adding a climatology for September.
City Name / Station ID: New York, NY (LaGuardia Airport – KLGA)
Local Geography and Topography
Station Elevation: 10 feet above sea level.
Station Location: LaGuardia Airport (KLGA) is situated on the north shore of Queens along the East River, approximately 6 miles east-northeast of Midtown Manhattan.
KLGA’s location within the broader NYC area, as seen in a Google Maps terrain view
Important Topographical Features: New York City is located in the extreme southeastern corner of New York State, bordering suburban New Jersey and Connecticut. These suburban regions combined with those in Long Island comprise the Greater New York City Metropolitan Area, which is the most populous urban agglomeration in the United States and one of the populous urbanized areas in the world with an estimated population of 18 million. New York City itself sprawls across the coastal plain around the Hudson River estuary. The terminal moraine formed by glaciers of the last Ice Age result in a ridge of higher terrain that cuts a swath from southwest to northeast across the boroughs from northern Staten Island, northern Brooklyn, southwestern through central and northeastern Queens. Otherwise, the city itself is low lying. This ridge varies in height between 200-400 feet, rising sharply from south to north, but tapering more gently north. North and west of the city (about 30-50 miles away), lie significant elevations of the Catskills (north), Poconos (west), Taconics that are part of the broader Appalachian Mountain Range. The elevations of the lower foothills can range from 1000-1500 feet. Some of the elevations in the Poconos and Catskills, west and north of KLGA respectively, peak between 2000-3000 feet. The open expanse of the Atlantic Ocean lies south of KLGA and New York City. Long Island Sound also lies east-northeast. The vast urbanized area of the NYC metropolitan region has significant effects on local microclimates via differential heating (urban heat island effect). KLGA is in a low-lying area sensitive to UHI effects and marine influences.
On winter mornings, ocean temperatures which are warm relative to the land reinforce the effect of the city heat island and low temperatures are often 10-20 degrees lower in the inland suburbs than in the central city. The relatively warm water temperatures also delay the advent of winter snows. Conversely, the lag in warming of water temperatures keeps spring temperatures relatively cool. One year-round measure of the ocean influence is the small average daily variation in temperature.
National Weather Service – NYC Office
Wind Patterns
Below is a wind rose – you can read more about how to interpret this chart here.
Frequency (percentage) of the single most common wind direction: Due northeast (9.5%).
Directions that are most and least common: Most common wind directions include due south (9%), due southwest (8.5%), and northwest (8%). Least common wind directions are east-southeast (1.5%), due southeast (2.5%), and due east (3.5%).
Direction(s) most likely to produce the fastest winds: Winds of 16.5-21.4 knots are most frequently found coming from due northeast, and due northeast. North-northwest, east-northeast, and due south directions can also see less frequent winds over 21.4 knots.
Direction(s) least likely to produce the fastest winds: As is the case with several other months, the least common wind directions of due east, east-southeast, and due southeast also rarely seen winds in excess of 16.4 knots.
Impacts of wind direction on local weather: September’s wind profile sees a shift away from the general pattern of the summer months preceding it (June, July, August) during which southerly winds are predominant, and during which due south is the single most common wind direction. April is the last calendar month when due south isn’t the single most common wind direction, so it takes quite a bit of time in order for winds to shift off this summer pattern.
The most common wind directions in September are almost evenly split between northeasterly and northwesterly and southerly and southwesterly winds in percentage terms of frequency. Northwesterly winds are notably more frequent, and faster northeasterly and northwesterly winds start to appear in September as opposed to the summer months. Northwesterly winds in general will bring cooler, drier Canadian air into the region following cold fronts. Northeasterly winds, on the other hand, are related to backdoor cold fronts sweeping from the Canadian Maritimes, the onshore flow ahead of an advancing warm front, or a passing coastal storm.
The continued downward trend in southerly winds is likely a reflection of the diminishing influence of sea breezes as average land temperatures cool while average sea surface temperatures are still close to their peak (though also cooling). The narrowing gap between these two will tend to reduce the potential for sea breeze circulations to set up. However, these sea breezes can still exert an influence on local temperature and can still provide boundaries for convection. Southwesterly winds are also similarly capable of bringing in oppressive heat, as seen in the temperature section below.
Maximum observed two-minute wind speed for the month: 44 knots (51 mph)
Temperature and Precipitation Averages/Records
Temperature units are in Fahrenheit and precipitation is in inches.
Worth noting: September can still offer up oppressive heat, especially in the first half of the month. The monthly all-time record high of 102°F is also the second highest record temperature recorded for the year at KLGA (August has the hottest record high: 104°F). September’s monthly precipitation record of 4.63″ in one day is also has the 3rd highest single-day precipitation record after April and August. While it can get quite hot in September, it’s also possible for temperatures to get cold too, with the record low for the month in the low-40s! Average high temperatures dip back below 80°F and average lows drop below 60°F again in September after the summer months, marking a definite fall feel.
Labor Day weekend is shaping up to be a good one overall in terms of sensible weather. A dry cold front passage today sets the stage for high pressure to take control over the remainder of the weekend. The only wrinkle is a warm front forecast to pass Monday that could bring some rain. Looking ahead into next week, a warm up should precede another cold front mid-week. The big weather story this weekend will be much further south of us, as Hurricane Dorian takes aim at Florida as a dangerous Category 4 storm.
Rest of today – sunny with high temperatures in the mid-upper 80s. Overnight lows in the upper-60s.
Saturday – high pressure starts to build from the west, which will result in a cooler weather with northerly winds. High temperatures topping out in the low-80s with lots of sun and overnight lows in the mid-60s.
Sunday – high pressure will progress east, giving us another pleasant day with lots of sun and comfortable temperatures in the low-80s. Overnight lows warm up in the upper-60s with a warm front approaching from the southwest.
Monday (Labor Day) – chance for rain during the day as a warm front, then a weakening cold front approach. High temperatures in the low-80s with mostly cloudy skies. Overnight lows around 70ºF.
Hurricane Dorian Heading Towards Florida
Over the course of the last few days, Hurricane Dorian made a pass over the Northern Lesser Antilles, hitting the Virgin Islands, and Martinique, but sparing Puerto Rico. This was a blessing for an island still recovering from the devastation of Hurricane Maria. However, because Dorian avoided the disruptive influence of high terrain in Puerto Rico, it entered the open waters of the Western Atlantic north of the island ready for continued intensification. Unfortunately, various forecast models have been consistently depicting Dorian making landfall somewhere in Florida early next week as a dangerous Category 4 hurricane packing max sustained winds of 140 mph.
Latest GOES visible satellite imagery of Hurricane Dorian
Overnight going into today, Dorian’s been steadily strengthening and is now showing a markedly more symmetrical structure than before, along with an eye developing in visible satellite imagery. This suggests that the southerly shear and dry air that was afflicting the storm yesterday has abated somewhat. At this point, there is nothing really stopping Dorian from continuing to strengthen to a major hurricane.
National Hurricane Center official forecast for Dorian as of 11AM Friday
Forecasters continue to have high confidence that Dorian will make a turn towards a more westerly direction as high pressure builds over Bermuda and keeps building to the west. This will block Dorian from taking a northerly route away from Florida. Worryingly, forecast models have trended towards a slower and more southerly track overnight, then a turn north after landfall. On this current track, a large part of Florida would be affected by the storm for a considerable amount of time, increasing the risk of damaging storm surge and inland flooding from prolonged heavy rain.
After a week of hot, humid weather and several bouts of strong to severe thunderstorms, we will finally get a break from both the heat and the rain just in time to enjoy the weekend. Behind a cold front that’s slowly pushing south, high pressure will build in and usher in a Canadian polar airmass that will bring a noticeable change to high temperatures – 10ºF cooler in most cases. Rain chances return late in the weekend period.
Rest of today – showers associated with a wave of low pressure moving along the cold front that passed last night should end by noon. Mostly cloudy with gradual clearing. High temperatures in the upper-70s and overnight lows in the mid-60s.
NAM (North American Model) forecast for 2 meter above ground level temperature Saturday at 2PM
Saturday – mostly sunny, high temperatures in the upper-70s, noticeably drier feel with dew points much lower than the past few days with Canadian high pressure taking over. Overnight lows in the mid-60s.
Sunday – below average temperatures continue with high temperatures in the mid-70s. By this time, the high pressure center will have shifted to the northeast and will thus enable cooler, more moist onshore flow to influence the weather. We should see more clouds and could even see some scattered rain showers. Overnight lows in the low-60s.
Weather Prediction Center surface forecast for 8AM Sunday
Monday – high temperatures in the upper-70s with partly sunny or mostly cloudy skies. An area of low pressure (which could become a tropical depression this weekend) off of Florida will track along the East Coast and should at the very least bring cloudier weather. Overnight lows in the mid-60s.
A stationary front stalled out southeast of the city over the Mid-Atlantic will be the primary agent responsible for an extended period of humid, cloudy, and unstable weather over the weekend. As was the case last weekend, temperatures will be on an upward trend from the low-80s into the low-90s by the start of next week.
Rest of today – mostly cloudy with isolated showers and thunderstorms particularly closer to higher terrain north and west of the city. High temperatures in the low-80s. Overnight lows in the low-70s.
Weather Prediction Center surface forecast for 8AM Saturday
Saturday – more clouds than sun with the stationary front just south of the area. Continued onshore easterly flow behind north of this stationary front will keep things cooler and humid. High temperatures in the low-80s. Chance for showers and thunderstorms to develop again in the afternoon hours with an unstable airmass (due to the high moisture content caused by the onshore flow) as heating increases. Overnight lows in the low-70s.
Sunday – temperatures begin to warm up into the upper-80s as winds shift towards the south. The stationary front attempts to move north as a warm front but high pressure is forecast to develop west of us and block this northwards advance. Scattered showers and thunderstorms are again possible in the afternoon hours. Overnight lows in the mid-70s.
GFS model 2 meter above ground level temperature, 10 meter above ground level wind forecast for 2PM Monday
Monday – with winds shifting to towards the southwest, much warmer air will advect into the region. High temperatures expected to top out in the low-90s with overnight lows in the upper-70s. Mostly sunny skies forecast with the high pressure building.
A couple stormy nights in the city the last couple days will give way to a superb weekend of mostly sunny skies and warm, but comfortable temperatures. High pressure will remain in control over the region’s weather going into next week. The next chance for significant precipitation won’t enter the picture until mid-week next week.
Rest of today – mostly sunny with high temperatures ranging 84-87°F. There is a slight chance for an isolated shower or thunderstorm later this afternoon with a weak disturbance pivoting through at the upper-levels. Forecasters cite the lack of any significant convective inhibition so storms could pretty easily get going, however, moisture content isn’t all that great. Overnight lows should be mild in upper-60s.
HRRR model simulated radar for 4:45PM today
Saturday – with a cold front passing today, we’ll have cooler temperatures tomorrow, high temperatures reaching only into the low-80s under mostly sunny skies. Overnight lows cooling into the mid-60s.
Weather Prediction Center surface forecast for 8PM Saturday
Sunday – just another beautiful day with mostly sunny skies and high temperatures in the low-80s. Overnight lows starting to warm back up into the upper-60s.
Monday – temperatures will warm back up as the high pressure center shifts east, and we get the warmer southerly, and westerly return flow. We should see high temperatures in upper-80s and overnight lows in the low-70s.
During my time taking classes as part of Penn State University’s Undergraduate Certificate in Weather Forecasting, we were taught that understanding the climatology of the location you are interested in is an important prerequisite for making accurate forecasts. This post continues on this theme, adding a climatology for August.
City Name / Station ID: New York, NY (LaGuardia Airport – KLGA)
Local Geography and Topography
Station Elevation: 10 feet above sea level.
Station Location: LaGuardia Airport (KLGA) is situated on the north shore of Queens along the East River, approximately 6 miles east-northeast of Midtown Manhattan.
KLGA’s location within the broader NYC area, as seen in a Google Maps terrain view
Important Topographical Features: New York City is located in the extreme southeastern corner of New York State, bordering suburban New Jersey and Connecticut. These suburban regions combined with those in Long Island comprise the Greater New York City Metropolitan Area, which is the most populous urban agglomeration in the United States and one of the populous urbanized areas in the world with an estimated population of 18 million. New York City itself sprawls across the coastal plain around the Hudson River estuary. The terminal moraine formed by glaciers of the last Ice Age result in a ridge of higher terrain that cuts a swath from southwest to northeast across the boroughs from northern Staten Island, northern Brooklyn, southwestern through central and northeastern Queens. Otherwise, the city itself is low lying. This ridge varies in height between 200-400 feet, rising sharply from south to north, but tapering more gently north. North and west of the city (about 30-50 miles away), lie significant elevations of the Catskills (north), Poconos (west), Taconics that are part of the broader Appalachian Mountain Range. The elevations of the lower foothills can range from 1000-1500 feet. Some of the elevations in the Poconos and Catskills, west and north of KLGA respectively, peak between 2000-3000 feet. The open expanse of the Atlantic Ocean lies south of KLGA and New York City. Long Island Sound also lies east-northeast. The vast urbanized area of the NYC metropolitan region has significant effects on local microclimates via differential heating (urban heat island effect). KLGA is in a low-lying area sensitive to UHI effects and marine influences.
On winter mornings, ocean temperatures which are warm relative to the land reinforce the effect of the city heat island and low temperatures are often 10-20 degrees lower in the inland suburbs than in the central city. The relatively warm water temperatures also delay the advent of winter snows. Conversely, the lag in warming of water temperatures keeps spring temperatures relatively cool. One year-round measure of the ocean influence is the small average daily variation in temperature.
National Weather Service – NYC Office
Wind Patterns
Below is a wind rose – you can read more about how to interpret this chart here.
Frequency (percentage) of the single most common wind direction: Due south (12.25%).
Directions that are most and least common: Most common wind directions include due southwest (10%), due northeast (9.75%), and south-southwest (8.75%). Least common wind directions are east-southeast (1%), due southeast (2.5%), and due east (2%).
Direction(s) most likely to produce the fastest winds: Winds of 16.5-21.4 knots are most frequently found coming from due northeast, and due south. It appears that due northeast also has some probability of exceeding 21.4 knots.
Direction(s) least likely to produce the fastest winds: As is the case with several other months, the least common wind directions of due east, east-southeast, and due southeast also rarely seen winds in excess of 16.4 knots.
Impacts of wind direction on local weather: August winds continue to exhibit a distinctive summer pattern, and share many of the characteristics of the wind profiles for June and July. Southerly and southwesterly winds are a touch less common in August versus July, while northwesterly winds increase in frequency slightly. Like in July, heat waves can accompany the clockwise return flow from the southwest when subtropical Bermuda highs set up southeast of the area. A slight down tick in the frequency of southerly winds may point to a decline in sea breezes, with sea surface temperatures continuing to warm and narrowing the gap with average air temperatures. Increases in northwesterly winds could be an indication of a stronger influence from Canadian high pressure.
Maximum observed two-minute wind speed for the month: 45 (52 mph)
Temperature and Precipitation Averages/Records
Temperature units are in Fahrenheit and precipitation is in inches.
Unsettled weather takes hold during the mid-week period as a couple prefrontal disturbances affect the area. The focus for heavier rain will be later Wednesday as a cold front approaches. Behind this cold front, conditions should improve and result in a pleasant, dry weekend.
Rest of today – mostly cloudy with a chance of isolated showers and thunderstorms later in the day as a shortwave trough lingers around the area. Temperatures in the mid-80s. Overnight lows in the low-70s.
Weather Prediction Center surface forecast for 8PM Wednesday
Wednesday – mostly cloudy with high temperatures in the mid-80s. Heavy rain possible especially later in the day with a cold front approaching. With a moist air mass in place, some thunderstorms that pop up could produce heavy downpours and localized flooding. Rain could continue overnight in more isolated form. Lows in the low-70s.
Thursday – brief subsidence behind the cold front that passes through Thursday should result in calmer weather and warmer temperatures with high temperatures in the upper-80s. Before that happens though, rain and thunderstorms can still pop up. Overnight lows in the low-70s.
Climate Prediction Center 6-10 temperature outlook valid Aug 11 – Aug 15 (this Sunday into next week)
Friday – cooler, sunny, with high temperatures in the low-80s. Overnight lows cooling into the upper-60s as Canadian high pressure begins to build.
After last night’s rains, we’ll see high pressure builds over there weekend. This will lead to mostly sunny and warm weather for the forecast period. A dry cool front passing Sunday won’t do much to cool things off. Instead, temperatures will continue an upwards trend into next week. It remains to be seen what sensible impacts the remnants of Tropical Storm Barry could have for us late next week.
Rest of today – warm, with mostly sunny skies. High temperatures in the upper-80s despite the cold front passing due to warning influence of downsloping westerly winds. Overnight lows in the low-70s.
Weather Prediction Center surface forecast for 8AM Sunday
Saturday – could see some high temperatures and sunny skies in the low-90s in denser urban areas away from the coast. Otherwise most areas in the upper-80s except at the immediate coast where a sea breeze should develop. Overnight lows in the mid-70s.
Sunday – mostly sunny with highs similar to Saturday in the upper-80s. Overnight lows in the mid-70s.
Looking ahead into the medium range, 6-10 day Climate Prediction Center temperature outlook for 7/17-7/27. Much of the country including our area looks set to see above average warmth.
Monday – yet another day of mostly sunny skies and high temperatures in the mid-upoer 80s. Overnight lows in the mid-70s.
