Category Archives: Storms

NYC Weekend Weather – Dec 21, 2018

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The official start of winter hits at 5:23PM EST, though you’d be forgiven for thinking it were a spring day instead, with temperatures well above normal and a driving rainstorm to end the week. The storm tapers off rather quickly. Cold air wrapping around the exiting storm will drop temperatures right back into normal ranges for the rest of the weekend and going into the week of Christmas.

Rest of today – bouts of heavy rain, which have already induced flash flood and flood warnings, will continue through the early afternoon hours. There should be a lull in activity as the first cold front that’s been bringing this heavy rain exits east. More rain is possible with a secondary cold front set to pass through later this evening and tonight. Strong winds are set to continue throughout the day as two areas of low pressure responsible for this storm consolidate and continue to deepen (hence inducing a large pressure gradient). High temperatures likely have already occurred today in the low-60s, and temperatures will slowly drop into the upper-50s. Overnight lows should still be quite warm, in the upper-40s.

High Resolution Rapid Refresh model simulated radar for 3PM

Saturday – the first full day of winter will see a return to more seasonable temperatures with highs in the mid-40s under mostly cloudy skies. Clouds will be slowly dissipating as high pressure builds in behind the exiting storm. Overnight lows will get back into the mid-30s.

Weather Prediction Center forecast surface map for 7AM Saturday

Sunday – mostly sunny day with high temperatures in the low-40s and overnight lows into Monday in the mid-30s.

Monday – another mostly sunny day anticipated with a high in the low-40s.

NYC Detailed Forecast for Saturday, Dec 15, 2018

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Saturday looks to be a dreary start to the weekend, however, it appears at this time that it’ll actually end up being the better half of the weekend. While rain chances exist for Saturday, the best conditions for heavier rain don’t look to materialize until Sunday. Even with clouds, rain, and winds shifting onshore from the east and northeast, Saturday afternoon may end up being the warmest day we’ve seen for quite some time. Below, I will provide a detailed forecast using KLGA (LaGuardia Airport) as a reference point. This is because KLGA will be easy to verify forecast outcomes for.

My Forecast
High: 51ºF | Low: 41ºF | Max sustained winds: 17 mph | Total precipitation: 0.13″ – verification for temperatures and precipitation will come from METAR data for the period between 1AM Saturday and 1AM Sunday (06Z Saturday to 06Z Sunday). Wind speed verification will draw on the daily climate summary.

Verification
High: 50ºF | Low: 45ºF | Max sustained winds: 24 mph | Total precipitation: 0.11″. Updated Sunday, December 16, 2018 1PM EST. Assessment: this ended up being a good forecast on precipitation and high temperature. However, I was too low on wind and low temperatures. Because of the light precipitation, little evaporational cooling occurred at the surface, where the air was nearly saturated most of the day, leading to warmer low temperatures. For winds, I may need to adjust my forecasts upwards for LGA when winds are out of the northeast because winds from this direction will flow over the open waters of the East River, with very little frictional drag.

Synoptic Set Up (The Big Picture)

A slow moving storm system with origins in the Deep South will make its way into the Northeast over the weekend. This storm will eventually transition to a coastal storm as it moves offshore of the Northeast. At the 500 mb level, this storm is driven by a closed low, which will almost nearly become completely cut off from the primary wind pattern (steering currents) at this level. This is what explains the slow forward progress of the storm. The result of this is that we’ll experience an extended period of cloudy and rainy weather this weekend. Low-level moisture appears to be maximized on Sunday, though, so Saturday may end up being a better weekend day.

Surface forecast from Weather Prediction Center, valid 7PM Saturday

High Temperature

MOS forecasts show high temperatures Saturday in the low-mid 50s, with NAM (North American Model) coming in at 53ºF and GFS (Global Forecast System) pointing to 56ºF. NBM (National Blend of Models) – a consensus based forecast model, showed highs of only 49ºF. I tend to side with high temperatures on the cooler side due to persistent low overcast clouds (discussed below), and an onshore northeasterly wind later in the day.

Low Temperature

The same MOS data above has lows on Saturday of 44ºF for NAM, 46ºF for GFS and 43ºF for NBM. I’m siding with the cooler side of the forecast envelope again due to the fact that precipitation will be ongoing overnight and there could be some evaporational cooling impacts to account for. Also, with the forecast period ending 06Z Sunday, I actually think the low for this period could be at the tail end, based on MOS. This would be after a prolonged period of onshore winds that I think could bring temperatures into the low-40s.

Max Sustained Winds

Although there will be precipitation during Saturday, as cited below, there looks to be a stable layer with a surface inversion during much of the day on Saturday (see the second Skew-T below). This will make downward momentum transfer during precipitation periods rather inefficient. The pressure gradient isn’t looking particularly strong either, since the low won’t be deepening until Sunday when it moves offshore. With these factors in mind, I think that a max sustained wind of 15 knots (17.25 mph) is reasonable.

Total Precipitation

This will be the trickiest part of the forecast. As is often the case with coastal storms, the gradient of precipitation totals is quite steep. There’s also considerable spread in ensemble models for total precipitation, leading to a low confidence in this forecast. A key factor here is that low-level moisture doesn’t look to be particularly robust as the day progresses (see graphic below). There’s also no clear lifting mechanism at the surface.

850 mb relative humidity, and wind at 1PM Saturday. Areas in blue are saturated, browns indicate very dry air, note how close that dry air is to NYC

While it’s clear that the day starts off with rain overnight, both GFS and NAM suggest that things will dry out a bit in the afternoon hours. That could translate to a lull in precipitation during that time frame.

NAM forecast sounding for 4AM at KLGA. Refer to my earlier post for a guide on how to interpret this Skew-T.
By 1PM, though, not that there’s a marked drying of the low levels above 850 mb. This could certainly cut into precipitation and result in light rain or even a lull in rainfall.

SREF probabilities of total precipitation and the best lift show that these remain south of the area, over the open waters of the Atlantic. However, the gradient is quite sharp for this, so any deviation northward on the storm track could throw a lot more rain our way.

SREF (Short Range Ensemble Forecast) forecast of strong lift (omega >= -9 microbar/sec). Lift is a critical ingredient in producing precipitation. I’ll explain in a later post 🙂


NYC Weekend Weather – Dec 14, 2018

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A slow moving storm system will bring a prolonged period of unsettled weather to the NYC region this weekend. The upside of this storm is that it will usher in some warmer air from the south, giving us some above average temperatures for a brief spell. Behind this storm system a cold front is forecast to pass through early next week and return us to below normal cold for this time of year. I will be following up on this post with a detailed forecast for Saturday, as I attempt to keep my forecasting skills sharp.

Rest of today – overcast, with high temperatures around 50ºF. Increasing chances for rain going into this evening and overnight. Low temperatures in the mid-40s overnight.

Surface forecast for Saturday morning, 7AM

Saturday – similar day to today with a generally gloomy feel, overcast skies with a chance for rain, though looks like precipitation will be on the light side. High temperatures in the low-50s. Overnight lows into Sunday cooler than Friday, in the low-40s.

Sunday – yet more rain possible with the storm slowly making its way east and transitioning to a coastal storm. High temperatures are expected to be cooler because winds will shift onshore from the northeast – highs probably in the mid-40s. Overnight into Monday, temperatures should hold in the upper-30s with rain chances winding down.


Surface forecast for Sunday at 7AM

Monday – skies slowly clearing with high temperatures in the mid-40s.

NYC Weekend Weather – Sept 14, 2018

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After a week of gloomy, cloudy, and at times rainy weather, we will get a nice break this weekend as conditions improve. The same high pressure that’s caused Hurricane Florence to make landfall on the Carolinas by blocking its northward progress will bring us sunnier weather. Indeed, some of the cloud cover over our area is actually a result of outflow from Florence. Its remnants will impact us with rain at some point early next week.

Rest of today – mostly cloudy with high temperatures in the mid-70s as winds continue from the east. High surf with waves 8-12 feet are possible at the coast due to Florence.

Saturday – decreasing clouds as high pressure continues to build. High temperatures around 80ºF.

Sunday – sunny, high near 80ºF, high pressure remains in control.

Monday – clouds and the chance for rain returns. More moist air returns as the high pressure that gives us nice weather over the weekend slides east (and the flow on its western side starts to bring moisture from the south up). We’ll need to monitor the progress of the remnants of Florence as they are likely to bring us rain.

 

NYC Weather + Special Tropical Update – Sept 10, 2018

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This week kicks off with a prolonged period of unsettled weather as a warm front and a cold front both impact the area. Chances for rain will be with us through Wednesday. Conditions finally improve late in the week. We luckily will avoid direct impacts (aside from high surf) from what will be an extremely dangerous Hurricane Florence, which looks set to make landfall on North Carolina late this week. Aside from Florence, two other storms pose threats to US territories this week.

Rest of today – cloudy, with periods of rain, heavy at times, especially later in the day towards the overnight hours. High temperatures will be in the upper-60s with cool, persistent onshore flow from the east. Ahead of an approaching warm front.

Tuesday – chances for thunderstorms will persist into Tuesday, with this slow-moving warm front finally pushing through. There could be thunderstorms overnight. Then, later in the day, as the trailing cold front moves through. Once the warm front passes over, we’ll be within the warm sector of the parent low pressure system, which will allow temperatures to climb into the low-80s with a marked increase in humidity.

Wednesday – the cold front mentioned above will slow down as it approaches us and dissipate. This will lead to continuing chances for rain, and thunderstorms with temperatures again in the low-80s.

Thursday – high pressure will finally begin to build in to our north by Thursday behind the cold front above. This will lead to better conditions, with partly sunny skies and temperatures in the low-80s.

Friday – partly sunny skies with high temperatures in the low-80s again with high pressure to our north.

Florence, Isaac, and Olivia All Pose a Threat to the US

These three storms have the potential to impact the Southeastern US, Puerto Rico, and Hawaii respectively within the next week. Among these, Florence is by far the most dangerous, as it could make landfall on North Carolina as a Category 4 storm with maximum sustained winds of 145 mph.

Hurricane Florence

Over the past day or so, the picture for Florence has become much clearer. Various forecast models have come into remarkable alignment on both the overall track and intensity of Florence over the next 5 days, which means bad news for the Carolinas. The picture looks grim, with Florence set to make landfall as a very strong Category 4 storm packing sustained winds of 145 mph. Florence has nothing but warm water ahead of it, and there should be minimal impact ot this storm from vertical wind shear. Even if the storm weakens due to eyewall replacement cycles prior to landfall, that would only serve to increase the radius of its damaging winds. No matter how you slice it, Florence is likely to bring deadly storm surge and risk of life-threatening flash flooding and inland flooding. The fact that its forecast track slows to a crawl after landfall makes the flooding risk inland especially serious.

Hurricane Isaac

Isaac is a compact storm, which is leading to some uncertainty regarding both its track and intensity forecast. Small tropical cyclones are subject to wild swings in intensity both ways, which can be unpredictable at times. As of now, Isaac is forecast to cross the Windward Islands of the Lesser Antilles as a Category 1 storm, then continue into the Caribbean where hostile shear conditions should cause it to weaken. It is worth noting, despite the UKMET model being an outlier, that there are some signals that the storm could turn to the northwest later in the period, which could mean a threat to Hispaniola and Puerto Rico.

Hurricane Olivia

This storm continues to track towards Hawaii. Although weakening due to the influence of moderate wind shear, it is still set to hit Hawaii later this week as a strong tropical storm. The primary threat to Hawaii from Olivia will be in the form of heavy rain and flash flooding regardless of whether it makes direct landfall on one of the main islands.

NYC Weekend Weather – Sept 7, 2018

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Cooler temperatures are finally upon us after a very hot and humid week. However, the cooler weather also brings a prolonged period of cloudy conditions, with chances for showers each day this weekend. Rain chances continue into the beginning of next week with a storm system approaching. Long-term, we look towards the tropics, as Tropical Storm Florence continues to have the potential for bringing some impacts to the area.

Rest of today – overcast, with much cooler high temperatures in the mid-70s. Chances for showers, especially later in the day.

Saturday – cloudy with high temperatures remain cool in the low-mid 70s with northeasterly onshore flow behind a cold front draped west-east south of us. This front (which passed through yesterday) will become stationary. Multiple impulses of energy will run along this boundary and allow for continued slight chances of showers.

Sunday – yet another cool, cloudy day with chances for rain. High temperatures around 70°F.

Monday – the stationary front stalled out south of us will return north as a warm front. As this happens, chances for rain increase, along with temperatures rising back into the mid-upper 70s.

Will Tropical Storm Florence Impact the East Coast?

Tropical Storm Florence has been active over the eastern and central North Atlantic for over a week now. Within the last few days, Florence underwent a rapid intensification that brought it up to Category 3 status, making it the first major hurricane of the 2018 Atlantic hurricane season. Subsequently, it has weakened to a tropical storm under relentless strong shear. However, it is expected to reintensify into a major hurricane once shear subsides. Worrying trends in the track forecast for Florence continue to allow for the possibility of landfall on the East Coast, or at the very least, substantial coastal impacts like dangerous surf and beach erosion. However, the National Hurricane Center continues to note that there is considerable uncertainty to the track forecast for Florence, such that it is still too early to determine what effects it will have on the East Coast. This storm will warrant careful observation over the coming days and I will have subsequent updates on it.

NYC Weather Update – Sep 4, 2018

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A brief break in the heat over the weekend has led back into another warm spell to begin this week. This latest blast of heat will be short-lived as a backdoor cold front sweeps through tomorrow, followed by another, stronger cold front later this week. Temperatures for the upcoming weekend will once again be comfortable, seasonable to below average. In the tropics, things are starting to get busy with tropical storms Florence and Gordon active and another tropical wave poised to become a tropical cyclone off the coast of Africa. Gordon will make landfall overnight on the Gulf Coast east of New Orleans.

Rest of today – hot and humid with temperatures in the low-90s, mostly sunny skies.

Wednesday – cooler, though still warm with high temperatures in the upper-80s and partly sunny skies. A backdoor cold front will bring cooling onshore southeasterly breezes that help keep a lid on temperatures.

Thursday – temperatures rise back a couple degrees into the low-90s ahead of an approaching cold front from the northwest. The warm air ahead of the cold front could help set the stage for a few scattered strong thunderstorms as the front passes through.

Friday – temperatures cool off quite a bit into the low-80s under mostly cloudy skies. Chance of showers during the day with the cold front lingering south of the area.

Tropics Heating Up

We have 2 active tropical cyclones (Florence, Gordon), and another incipient one in the Atlantic Basin. Tropical Storm Gordon could strengthen into a hurricane before landfall on the Gulf Coast between Mississippi/Alabama overnight into Wednesday. Heavy rain could induce flash flooding in southern portions of these states. The immediate coastline will be at risk of storm surge flooding. Florence doesn’t pose an threat to land. The disturbance shown below that’s furthest east is a tropical wave that’s just emerged off the coast of Africa. This is worth watching as it has a high chance of becoming a tropical cyclone and its eventual track could pose a threat to portions of the Lesser Antilles.

NYC Weather Update – Aug 6, 2018

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This week starts off with a heat wave, with high temperatures expected to top 90°F up through Wednesday. A chance or showers and thunderstorms Wednesday will not bring too much in the way of relief from the heat and humidity. The air mass behind the cold front moving in Wednesday is only slightly cooler and less humid than the one in place now.

Rest of today – hot, humid, with high temperatures in the low-mid 90s.

Tuesday – more of the same, hot, humid weather with highs in the low-90s. A chance exists for some scattered showers and thunderstorms late in the day.

Wednesday – more organized showers and thunderstorms are expected to pass though late in the day Wednesday and overnight into Thursday as a cold front approaches from the west. High temperatures ahead of the front are expected to be in the low-90s again.

Thursday – a chance for leftover a shower or thunderstorm exists early, then improving conditions with high temperatures in the upper-80s and mostly sunny skies.

Friday – looking sunny now, with highs in the upper-80s.

NYC Weekend Update – Jul 20, 2018

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Last weekend’s beautiful, sunny weather will be but a fleeting memory this weekend as a coastal storm hits the area late Saturday going into Sunday. Periods of heavy rain and even some severe weather are possible Saturday night and Sunday, with the potential for isolated flash flooding. Unsettled weather continues into next week with a tropical weather pattern setting up providing daily chances for showers and thunderstorms.

Rest of today – a great start to the weekend, with high temperatures in the low-80s and sunny skies.

Saturday – cool, with high temperatures only in the upper-70s due to the influence of easterly winds ahead of a warm front attached to the advancing coastal storm. Clouds increasing late in the day and rain chances picking up in the evening hours going into overnight. Chance for heavy rain, scattered thunderstorms with gusty winds (even an isolated tornado possible). Gusty east winds will make the overnight hours feel particularly cool and miserable.

Sunday – rain chances continue into the day and even Sunday night. Temperatures increase behind the passage of the warm front mentioned above and winds shifting to the south – high temperatures should be in the mid-80s with mostly cloudy skies. All told, we could be looking at widespread rainfall totals of 1-3″ across the area.

Monday – showers likely again as temperatures remain in the mid-80s under mostly cloudy skies. A strong upper-level trough will be wedged between two areas of high pressure. The one off to our east over the western North Atlantic will continue to strengthen over the course of the week, blocking the eastward advance of this upper trough. This effectively will result in an extended period of southerly flow, with moist, tropical air coming our way. Multiple impulses of energy are expected to travel along this strong upper-level trough. Each one will bring with it a chance for showers and thunderstorms. This pattern does not appear to break until next weekend, although it’s not as though each day will be a washout either.

 

NYC Weekend Weather – Jun 22, 2018

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We got to enjoy one weekend last week where it didn’t rain at all. Unfortunately that won’t be the case this week with a storm passing through tomorrow. Temperatures will be cool with the influence of an onshore easterly wind before the passage of a warm front that will bring the chance for rain and thunderstorms.

Rest of today – cool, cloudy, with a high in the mid-70s.

Saturday – cloudy, with chances for rain and thunderstorms especially later in the day. The best chances for thunderstorms come with elevated convection late in the day and going into the overnight hours as a warm front approaches from the south. Temperatures will be cool in the mid-70s again.

Sunday – improving conditions with warmer temperatures in the warm sector after the passage of the warm front. Highs should reach into the mid-80s, possibly higher depending how much sun we get.

Monday – Canadian high pressure returns in the wake of this weekend’s storm and gives us sunny weather with mild temperatures in the low-80s.