Tag Archives: flooding

NYC Extreme Flash Flooding Event: Remnants of Ida – Sept 1, 2021

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It’s been a long hiatus for me posting content to this blog. Been a bit preoccupied with everyday life, but getting back into the swing of things with a detailed meteorological summary of the tragic and deadly extreme flash flooding event that took place on the evening of Sept 1, 2021. Credit for this goes in part to my friend and colleague Phil Lutzak, a fellow graduate of the PSU World Campus Weather Forecasting Certificate Program.

Synopsis

In this overview of the NYC flooding event of September 1st, 2021, the main goal is to ascertain why such severe flooding occurred in light of the preceding and concurrent weather conditions for that day. While it was quite well forecast by the NHC and NWS office forecasts in terms of a significant flood threat, clearly no national office could pinpoint the areas that would suffer the worst flooding until the day of the event when it was much clearer where the heaviest rains would be falling, nor could they possibly have gotten the exact severity correct given current forecasting capabilities. In hindsight we will examine the existing conditions during and just before the most intense period of the flooding and try to determine which developing synoptic and mesoscale parameters gave the most clues as to why much of the worst flooding conditions would be directly within the New York City metropolitan area.  

Forecasts Leading Up to the Event

There was a misconception after the event that the meteorological community failed to forecast the possibility of this event occurring. In fact, National Weather Service Weather Prediction Center had a solid grasp of the risks associated with the post-tropical remnants of Ida, having issued a high risk for flash flooding for areas of the Mid-Atlantic and Southern New England in the early morning hours of Wednesday, 01 Sept 2021 (4:20 AM EDT). 

The forecast discussion behind this excessive rainfall outlook was chilling in its prescience, specifically citing the possibility of deadly flash flooding and 3-8” rainfall totals. 

At 3:22 PM EDT, WPC issued Mesoscale Precipitation Discussion #0925, with the accompanying image:

In MPD #0925, WPC forecasters referenced 2-3+” per hour rainfall rates being possible due to a combination of factors, most notably very strong low-mid level forcing via frontogenetical influences and highly efficient, deep layer warm/tropical rain processes – a characteristic of Ida’s hybrid tropical/extratropical nature. 

The importance of Ida’s unique blend of tropical transitioning to extratropical character is also underscored in MPD #0923, in which WPC forecasters discuss the presence of a developing south-southwesterly low-level jet. This feature would reach peak strengths of 35-55+ knots at the height of the event, and became a critical ingredient in creating the exceptionally efficient moisture transport into the NYC area, shown in the following sections.  

By 9:28 PM that evening, the worst-case scenario envisaged by forecasters leading up to the event came to fruition and the NWS OKX office issued its first ever Flash Flood Emergency for NYC, containing the emphatic “THIS IS A PARTICULARLY DANGEROUS SITUATION” wording…

Meteorological History

Surface Conditions 

The following chart shows the radar representation and surface charts of the 48-hour progress of tropical depression Ida from the lower Mississippi valley into the Tennessee and Ohio River valleys and then into the mid-Atlantic and northeast regions. In the middle image it is clear that the heaviest precipitation was reduced as its inflow was becoming detached from the very moist Gulf of Mexico. The third, rightmost image shows how the tropical low, now merging with the warm front, was elongating north to south but at the same time tapping into a very moist airflow from the Atlantic Ocean, strongly enhancing the area of heaviest precipitation near the center of lowest pressure.     

Low and Mid-Level Conditions

While the high precipitation producing ability of tropical depression Ida was still in evidence, the position of its southerly flow in relation to the fairly stationary warm front allowed for maximum isentropic lift to focus right over NYC and surrounding areas, with much of the convection moving in from the south still having high precipitation producing energy powered by high theta-e tropical inflow. 

Here’s the MUCAPE analysis from 0200 UTC showing 1,000-2,000 J/kg positioned over NYC,

… and the following showing the extremely high 850 mb level moisture transport over the NYC area at 0200 UTC.

The 925-850 mb frontogenesis chart shows clearly where maximum frontogenesis was occurring

and the surface moisture convergence and DMC charts show, not surprisingly, that a maximum for surface and deep moist convergence was occurring over NYC and surrounding areas.

Mid to Upper Levels

This situation was one of the clearest examples of how baroclinic forcing can convert a weak or decaying tropical cyclone into an extremely prolific rainmaker. The 500 and 300 mb conditions were critical in allowing this approaching tropical low to make a fairly quick transition to a strong extratropical low. The result was the previously discussed extremely high moisture convergence right over the city. 

The 300 mb chart from 8PM EDT shows the right rear entrance region of a quite strong jet streak for late summer (100-120 knots) moving into position almost directly over the low which was just southeast of the NYC area, allowing for maximum divergence above the low center as it was merging with the warm/stationary front. This allowed for very high divergence to position over an equally strong low level convergence zone. 

In addition, the 500 mb analysis shows an ideal placement of the area just east of the trough base over the lower-level low circulation to allow strong upper-level divergence, resulting in intensification of the transitioning surface low.

All levels

For one final view that ties activity at the previous levels together, here’s the ARL simulated skewT diagrams for 0100 and 0200 UTC at New York City that evening. Clearly the atmosphere was saturated throughout with very high theta-e values at the lowest levels. 

Conclusion

From the NY Times, September 2nd, 2021: 

The rain broke records set just 11 days before by Tropical Storm Henri, underscoring warnings from climate scientists of a new normal on a warmed planet: Hotter air holds more water and allows storms to gather strength more quickly and grow ever larger. 

In New York City, the dead ranged in age from a 2-year-old boy to an 86-year-old woman, the police said. Some drowned in basement apartments in Queens, where a system of makeshift and mostly illegally converted living spaces has sprung up. 

Below are two dramatic images of the flooding in NYC. On the left is severe subway flooding that occurred in lower Manhattan (courtesy NY times). At right are multiple stranded vehicles on the Major Deegan Expressway in the Bronx borough of NYC (courtesy Craig Ruttle/AP).

It’s likely not possible at this time, nor in the near future, to use RAP or any of other quickest analytical tools to anticipate imminent flooding at the smallest mesoscale any more than we are currently able to. At this stage of the science, the most skilled forecasters use the best modeling tools currently available along with their own invaluable experience in watching unfolding precipitation patterns on radar loops and, combined with mesoscale graphics such as we have displayed here, anticipate where the heaviest precip is moving and whether it will intensify, weaken or remain stable.      

In light of this, a critical takeaway is to encourage better education of the public about what an “Emergency” and what a “Particularly Dangerous Situation” mean in practical terms. In other words, when the public receives an EAS alert with these terms in it, they need to be acutely aware of what preventive actions to take immediately rather than just dismiss this as another alert that probably won’t affect them. One other challenge with this system is that these alerts are often only translated to only one or two other languages. This is a problem for a city with hundreds of thousands of immigrants speaking myriad languages, many of whom are not literate in English, as this renders these vital, lifesaving alerts essentially useless to a wide range of the public, with predictably tragic consequences. 

NYC Detailed Forecast for Apr 19, 2019

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It’s been four months (!!) since I’ve done one of these detailed forecasts. I’m a bit out of practice but trying to get back into the groove. Lucky for me, I picked a day to forecast that has a decent bust potential for precipitation. I’ll discuss that below.

Friday is going to start off decently enough. It should end up being the warmest day of the week. However, it’s also going to be the start of a protracted period of unsettled weather that will affect the weekend. A flash flood watch is in effect late overnight Friday going into Saturday for this reason.

My Forecast
High: 70°F | Low: 58°F | Max sustained winds: 30 mph | Total precipitation: 0.10″ – verification for temperatures and precipitation will come from METAR data for the period between 2AM Friday and 2AM Saturday (06Z Friday to 06Z Saturday) at LGA. Wind speed verification will draw on the daily climate summary from the National Weather Service.

Verification
High: 76°F | Low: 56°F | Max sustained winds: 24 mph | Total precipitation: 0.16″ – I did decently forecasting the low, and the total precipitation. Hedging way down on precipitation totals towards the NAM solution on a slower moving storm was a good idea. On the low temperature, I think a 2°F margin is acceptable here. Being off by 6°F on the high temperature here constitutes a forecast bust that I’ll put a post-mortem together for – as it turns out the bust happened here and not with precipitation. Winds were also not as strong as anticipated. I should have hedged a bit down too with less intense precipitation anticipated.

Weather Prediction Center surface forecast for 8PM Friday

Synoptic Set Up
We begin the period in the warm sector of a low with a center forecast to sit over southwestern Quebec. A secondary surface low is forecast to form over the OH valley and strengthens as it briefly moves northeast. This low is then forecast to stall out and retrograde northwest as it matures and occludes. This will lead to a protracted period of precipitation, with the primary focus being along a cold front moving through Sat morning. This may result in the best chance for heavy rain being outside the forecast period.

At the 850 mb level, a strong low-level jet will provide efficient moisture transport. At 500 mb we’ll be downstream of a longwave trough, with an embedded closed low that becomes cutoff (this mid-level cutoff low will be tied to why the secondary surface low retrogrades). The best vorticity and divergence (lift) associated with this upper low seems to move through after forecast period according to NAM forecast model. GFS has a bit earlier timing, and hence brings precipitation in earlier Friday. Finally, at the 300 mb, there’s not much evidence of enhanced divergence and lift at this level since, we’ll be east of any favorable entrance/exit regions of a 300 mb jet streak.

NAM forecast model’s depiction of the 500 mb layer at 11PM Friday. The cut off low referenced above is circled in green. The shades of yellow-purple indicate increasingly strong vorticity, which is linked to divergence and enhanced lift.

High Temperatures
GFS and NAM MOS are in pretty close agreement here. It should be warmer than average, since we’ll be in the breezy warm sector of a low as mentioned above. Limitations on warmth will be evaporational cooling due to precipitation, but this doesn’t appear to be a factor until late in the forecast period, past normal times for peak temperatures. The other factor is thick cloud cover. However, temperatures will largely be driven by warm advection tomorrow and not necessarily solar heating. EKDMOS suggests a temperature over 70ºF. In deference to this ensemble model, I’ve sided with the warmer GFS and EKDMOS (as well as National Blend of Models) and call for a high temperature of 70ºF.

  • GFS MOS output
  • NAM MOS output

Low Temperatures
NAM and GFS MOS are again in close agreement. With warm advection happening during the course of the overnight hours (strong winds at large angles to isotherms, southerly flow), have no reason to disagree that temperatures could actually go up early then back down a touch before rising again with daybreak, and I’m going with an overnight “low” of 58ºF that is well above average for this time of year.

NAM showing temperature contours and wind direction/speed for 2AM Friday. Note the direction of the wind barbs (pointing from south) is crossing at large angles of relatively closely packed isotherms. This is a set up favorable for warm advection (transport of warm air).

Max Sustained Winds
NAM is lower on winds than GFS, but the ensemble EKDMOS skews towards faster GFS solution. This makes sense with heavy rain possible and downward momentum transfer. Winds are forecast to back from south-southwest to south-southeast during the period. These directions don’t typically produce the strongest winds climatologically. However, a strong 45-60 knot low-level jet aloft mixing down with precipitation could easily top 20 knots, especially if elevated convection and thunderstorms materialize. I’m going with the EKDMOS 50th percentile range and going with 25 knots.

  • The NAM forecast sounding at 5PM tomorrow shows considerably drier low-mid levels.
  • In contrast, the GFS forecast sounding shows a deep saturated layer indicative of ongoing precipitation by 5PM tomorrow.

Total Precipitation
There’s a large spread between NAM and GFS on forecast totals (more than 0.50″) because the GFS is coming in with precipitation starting much earlier in the forecast period than the NAM. The local forecast office seems to buy more into the NAM solution due to its consistency with slower onset of heaviest precipitation. There is some indication as well of MUCAPE present in SREF plumes, could result in some elevated convection that would boost precipitation totals. Any faster timing and/or burst of elevated convection could cause heavier rain to fall earlier, resulting in a forecast bust.

Counting against that, I don’t see any strong signal for frontogenesis at the 850 mb level enhancing lift. SREF doesn’t show too much in the way of strong lift either. Still, the fact that SREF ensemble shows much heavier precipitation totals are not far off to the west during this forecast period makes me a bit nervous.

Lastly, moisture isn’t a total lock, and there’s some evidence of drier air offshore and pockets of dry air moving through from the west at times. NAM is notably drier than GFS at both outset of the forecast and throughout the forecast period, as seen in the comparison forecast soundings above. Training of storm cells possible with steering currents set up parallel to the forecast orientation of the cold front.


Cyclone Idai Synopsis and Aftermath

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Tropical weather is not often on our minds at this time of the year, since the Atlantic Hurricane season is still months away. But there are other active tropical basins at this time – last week Cyclone Idai spawned in the Southwest Indian Ocean and brought devastation to vast swathes of Mozambique, Zimbabwe, and Malawi. With 700 deaths already attributed to it, Cyclone Idai is one of the deadliest tropical cyclones to have impacted southern Africa on record. Sadly, that death toll could continue to increase as floodwaters recede, revealing the full extent of damage from the storm. In this post, I’ll take a look at why Cyclone Idai was able to grow so powerful, and why it caused such serious flooding.

Meteorological Synopsis

Idai formed as a tropical depression in the Mozambique Channel on March 4, 2019. It moved onshore shortly thereafter and spent several days over Mozambique as it executed a cyclonic loop. During this time, it managed to retain tropical characteristics (keeping a warm core), before it exited again over the open waters of the Mozambique Channel. As it continued moving east, it encountered increasingly favorable conditions for intensification with very warm sea surface temperatures and decreasing vertical wind shear.

  • Visible satellite image of Cyclone Idai close to when it made landfall on March 14, 2019
  • Track map of Cyclone Idai. The purple dot indicates where Idai first formed, and the green dot is where it lost tropical characteristics

For more details on the images above see the Wikipedia article about Idai.

A subtropical ridge began forming and strengthening over eastern South Africa, causing the cyclone to start turning west and heading towards the coast of Mozambique again.

As Idai moved west, it underwent 2 distinct periods of rapid intensification in response to the favorable conditions found over the Mozambique Channel during this time. In between, it experienced an eyewall replacement cycle, where it temporarily weakened as concentric eyewalls formed, and the inner one eventually collapsed as the outer one took over.

  • Upper level divergence at 18 UTC on March 14, 2019
  • Low level convergence at 18 UTC on March 14, 2019
  • Vertical wind shear analysis at 18 UTC on March 14, 2019

Unfortunately for those in Idai’s path, it regained strength after a second eyewall replacement cycle as it approached landfall because conditions continued to be quite favorable. The analyses above with satellite overlays valid for 18:00 UTC March 14, 2019 show the cyclone near its peak intensity under nearly ideal conditions (lower left of the image). The first two analyses show strong upper level divergence and low level convergence around Idai respectively. This indicates that upper level outflow was well established, which is also visible from the symmetrical presentation of the cyclone visually, with outflow channels evident. Upper level outflow is required for “ventilating” intensifying cyclones and helping them grow/maintain their intensity. That’s because as the storm gathers strength, low level convergence intensifies as winds in the storm pull air from surrounding areas inwards towards the eye of the storm. This convergence is what powers the intense thunderstorms in the eyewall. Without upper level divergence, the air converging at the storm’s core would continue building up, eventually resulting in rising pressure and a weakening storm – pressure, after all, is a measure of the mass of air over a given area.

The last image shows that Idai was also in a zone of very low vertical wind shear, between 5-10 knots during this time before landfall. Low vertical wind shear helps preserve the structure of a tropical cyclone. Unlike with severe thunderstorms, wind shear can actually shift the core of the strongest thunderstorms away from the center of a tropical cyclone’s center of circulation. That often marks the beginning of the end for a tropical cyclone. In the case of Idai, low wind shear let it strengthen considerably close to landfall, although it did weaken a bit right before landfall due to increased shear and interaction with land.

Why Such Devastating Flooding from Idai

While powerful storm surges accompanied Idai, the worst impact from Cyclone Idai was widespread catastrophic flooding in Mozambique and in Zimbabwe. Part of this comes down to the geography of the area impacted, with a broad, flat flood plain between Pungwe and Buzi Rivers, and with parts of Beira, the largest city in the area, lying below sea level.

European Space Agency satellite image, with areas in red indicating inundation taken earlier last week

As Dr. Jeff Masters pointed out in a post on Weather Underground, another big reason why Idai caused such serious flooding was because of the storm’s slow forward progress. This came down to the storm being embedded in an environment with weak steering currents.

CIMSS deep layer mean steering (250-850 mb) analysis loop of the Indian Ocean. Cyclone Idai is visible in the lower left corner.

In the animated loop of 250-850 mb deep layer mean steering winds, we see that as Cyclone Idai traversed the Mozambique Channel, it was in an area of very light steering winds (very few streamlines, few arrows on those streamlines). Mature tropical cyclone motion is influenced by winds in this layer of the atmosphere because these winds impact the tall thunderstorms in the cyclone’s core. When steering currents break down as in the loop above (a ridge with anticyclonic flow dissipated north of Idai), a tropical cyclone will start to slow down and sometimes can meander. In this case, with Cyclone Idai, a slower moving storm led to a prolonged period of heavy rain over the impacted areas. Had steering currents remained stronger, Idai would have produced less heavy rain over the same areas during a shorter window, likely reducing flooding impacts considerably.

Consider Donating to Support Recovery Efforts

The affected countries of Mozambique, Malawi, and ZImbabwe simply do not have the financial and physical resources to respond to a disaster of this magnitude. There are many worthwhile NGOs on scene providing relief aid. Please consider making a contribution to support these efforts, as the recovery effort will take years to complete. International Rescue Committee, Doctors Without Borders

NYC Weekend Weather – Aug 10, 2018

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Enjoy the pleasant weather today if you can, because conditions will deteriorate going into the weekend. Wet weather will impact the NYC region starting tonight, lingering well into early next week. Rain could be heavy at times, and flash flooding is a possibility. Temperatures during this time will be considerably cooler than this past week with the influence of clouds and rain. We will be stuck under the influence of multiple shortwaves moving through at the upper level during this time. Starting next week, forecast models suggest that a closed 500 mb low will form, then linger in the area due to strong downstream ridging (high pressure) over the western North Atlantic. This cut-off upper level low will provide for persistent unstable conditions conducive for multiple rounds of rain and thunderstorms. I will be off the next two weeks on vacation and will not be posting updates unless there’s severe weather forecast for the area.

Rest of today – increasing clouds as a cold front approaches the area from the northwest but stalls out and dissipates overnight. High temperatures in the upper-80s. Chances for showers and thunderstorms increase overnight.

Saturday – multiple chances for showers and thunderstorms, starting early in the day, then again in the afternoon and evening hours. Much cooler with mostly cloudy skies and high temperatures only in the mid-70s. The cold front that passed through yesterday will return north as a warm front. Ahead of this, winds will be easterly and onshore, bringing the cool, damp influence of the Atlantic over the area.

Sunday – warmer with high temperatures in the low-80s but still mostly cloudy. Chances for rain throughout the day as the frontal boundary above remains in the area.

Monday – yet another impulse of shortwave energy aloft brings a surface low towards the area, so rain chances persist with a shot for thunderstorms as well. Mostly cloudy with highs in the low-80s.

NYC Weather Update – Apr 16, 2018

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This work week starts off with a serious soaking rain from a storm system that has impacted a wide swath of the southern US with multiple days of severe weather. Conditions improve tomorrow and Wednesday before another chance for rain on Thursday. The rain this morning has led to the issuance of flash flood warnings, and numerous reports of flooding have already come in, so take caution out there, especially if you’re out on the roads.

Rest of today – rain, heavy at times, with the threat for flash flooding and flooding possible as storms train and hit the same areas repeatedly. Some embedded thunderstorms have been occurring this morning, enhancing the heavy rainfall potential. Some areas could see rainfall rates of up to 1″/hr along with gusty winds in the 40-50 mph range. Temperatures will be rising into the upper-50s as a warm front approaches from the south.

Tuesday – improving conditions as the storm system responsible for today’s rain moves off. Cooler, with temperatures maxing out in the low-50s in the wake of a cold front and mostly cloudy skies.

Wednesday – the best day of this week with high temperatures in the mid-50s and mostly sunny skies.

Thursday – another storm system, albeit weaker, will impact the area. High temperatures should hover in the mid-50s with chances for rain and cloudy skies otherwise.

 

NYC Weather Update – Apr 3, 2017

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wwwThe first week of April kicks off with multiple rounds of rain. Two separate storms are expected to bring drenching rains on Tuesday and Thursday. There may be some minor flooding concerns with 1″ of rain possible out of each system, on top of the rains we received last week.

Rest of today – cloudy, mild, with high temperatures in the upper-50s. Not a bad day for the Mets season opener.

Tuesday – late Monday, rain starts moving in ahead of an advancing warm front. Rain should begin around 10PM this evening and pick up in intensity overnight. Some thunderstorms are possible. Rain continues through most of the work day Tuesday, with some heavy rain possible. Mild again with high temperatures in the upper-50s.

Wednesday – brief respite between two storm systems, a gem of a spring day with high temperatures in the low-60s and mostly sunny to clear skies.

Thursday – temperatures cool off into the low-50s as the second storm system of the week impacts us and brings us yet another round of moderate to heavy rains.

 

NYC Weather Update – Jan 23, 2017

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Main weather headline to start the week will be a potent and slow-moving coastal storm bringing a variety of hazards to the region later today through tomorrow morning. This storm is the same one responsible for this weekend’s deadly tornado outbreak down south. Conditions improve dramatically towards mid-week.

Rest of today – a flood watch, coastal flood advisories, and high wind warning are in effect mostly through tomorrow morning. Cloudy with high temperatures steady around 40°F. Winds continue to increase throughout the day as a strengthening coastal low approaches and the pressure gradient between it and a high pressure center over Quebec tightens. A low-level jet will enhance winds. Sustained east and northeast winds of 30-40mph with gusts between 50-60mph will become commonplace late today and overnight. The strongest winds will occur closest to the coast.

Along with the strong winds, periods of heavy rain will bring the potential for 1-3″ of precipitation, which could lead to minor to moderate urban and small stream flooding. Timing of the onset of rain will be around 3pm this afternoon.

The persistent and strong northeast winds off the water will contribute to minor to moderate coastal flooding. This will be exacerbated during a couple of high tide cycles.

High resolution rapid refresh model simulated radar output for 3PM this afternoon

The storm approaching spans the better portion of the entire East Coast

Tuesday – rain and wind abate during the day, tapering off by the afternoon. High temperatures about the same as today in the low-40s.

Wednesday – as the coastal storm continues to pull away, temperatures rebound and mostly sunny skies return. High temperatures anticipated around 50ºF.

Thursday – another nice day with high temperatures in the upper-40s and mostly sunny skies.

 

NYC Weekend Weather – Jul 28, 2016

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We finally get a break from the heat along with some much needed rain in the next few days. Saturday looks to be the best day of the weekend. High temperatures this weekend will range anywhere between 15-20ºF cooler than last weekend. 

Overnight – lows in the mid-70s as a low pressure center passes almost directly over NYC. Because the low will be right over us, the main area of the heaviest rain will remain north of the city.

Friday – showers punctuated by periods of steady, heavier rain as bands of rain develop and wrap around the low pressure center as it tracks east. High temperatures in the low-80s with overcast skies. This low pressure system will thrive off the humid, tropical airmass in place over the region. A flash flood watch has been issued to reflect the possibility of some areas receiving 1-2″/hour rains. Embedded thunderstorms are possible, but are unlikely to reach severe limits. The bulk of the rain will fall overnight into the morning hours, and should begin tapering off in the afternoon from west to east. 

Screen Shot 2016-07-28 at 6.53.30 PM fill_94qwbgSaturday – high pressure passes briefly giving us a mostly dry day with partly sunny skies with highs in the mid-80s.

Sunday – another disturbance pushes through from the south providing more chances for rain and thunderstorms. Mostly cloudy with highs in the low-80s otherwise.

Screen Shot 2016-07-28 at 6.55.33 PM

Monday – skies gradually clear and temperatures warm back into the low-mid 80s.

Tuesday – warm and sunny with highs again in the mid-80s

Drought Conditions Forecast to Persist

Despite the rains this weekend, many parts of the area remain under a moderate drought, having received only about 25% of normal precipitation for this past month. The outlook for the season calls for persistence of drought conditions as below normal to normal precipitation will be insufficient to break the drought.

season_drought

NYC Weekend Weather – Aug 20, 2015

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Unsettled weather will be a trend for the end of this week and into the weekend as a cold front pushes through the region. Friday is shaping up to be the worst day with heavy rain with a risk for flash flooding. Conditions improve somewhat Saturday and Sunday, although a chance for showers and thunderstorms cannot be ruled out either day.

Rest of today – slight chance of showers or thunderstorms persists through this afternoon, though the best chances remain west of the Hudson, as was the case yesterday. We’ve hit a humid highin the mid-80s with a mix of sun and clouds above.

Friday – a cold front will be pushing through during the course of the day Friday. As the frontal boundary approaches overnight and into the early morning hours Friday, a slow moving band of heavy rain is expected to form and track from north to south across the area. It appears likely that the heaviest rain will fall in a narrow band during the early morning hours, and that things may already be drying out by the AM rush. High temperatures will be cooler than average with the cloud cover and rain, near 80.

Satellite image of the storm that will be bringing us some heavy rain Friday
Satellite image of the storm that will be bringing us some heavy rain Friday

High resolution rapid refresh simulated radar for 3AM EDT Friday
High resolution rapid refresh simulated radar for 3AM EDT Friday

A chance for showers and thunderstorms continues through Friday. By the end of the day, some areas could pick up between 1-2″ of rain, raising the risk of some flash flooding.

Saturday – although high pressure will be building once the cold front passes on Friday, a chance of showers and thunderstorms continues on the backside of this front. Temperatures will again be below normal with mostly cloudy skies and a high in the low-80s.

 

noaad3

Sunday – showers and thunderstorms cannot be ruled out for Sunday, which will end up being nearly identical to Saturday in sensible weather with high temperatures in the low-80s and mostly cloudy skies.

NYC Weather Update & TS Bill – Jun 16, 2015

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We’ve certainly seen plenty of rain during the month of June, yet the NYC region remains in an area of moderate drought as of last Thursday. However, this does not reflect the rain that fell overnight Sunday into Monday. After a gloomy start to the week, we get a break of decent weather tomorrow, before another possible round of rain Thursday. The week ends with some drying out and improving conditions.

Rest of today – highs should top out in the upper-70s to around 80 today, with the potential for showers and thunderstorms later this afternoon. Storms have already formed to our west over northeastern Pennsylvania, but there is a stabilizing marine air layer over NYC and points east, so these storms may yet break apart before reaching us.

 

High Resolution Rapid Refresh model simulated radar for 1PM today.
High Resolution Rapid Refresh model simulated radar for 1PM today.

Wednesday – skies will clear rapidly overnight and lead to a sunny, dry, and pleasant day on Wednesday. Highs should be near 80. The high pressure creating these pleasant conditions will not stay around long, as another warm front approaches from the west.

Thursday – will look a lot like today, with mostly cloudy skies, and a potential for showers and thunderstorms in the afternoon as a warm front nears the region. Highs will be a bit cooler in the mid-70s with the influence of clouds and a southeasterly flow off the ocean ahead of the warm front.

Friday – the warm front from Thursday is followed quickly by a cold front passing Friday morning. Behind this, high pressure takes control and brings decent weather for the first half of the weekend. Highs Friday should be in the low-80s with clouds and sun.

 

Tropical Storm Bill

Over the weekend, a disturbance organized over the western Gulf of Mexico, and by last night it had consolidated and intensified enough to be designated the 2015 Atlantic Hurricane Season’s second named tropical cyclone – Tropical Storm Bill. Bill will be making landfall imminently in Texas as a moderate strength tropical storm with maximum sustained winds of 60mph.

Satellite image of Tropical Storm Bill about to make landfall on the central Texas Gulf Coast
Satellite image of Tropical Storm Bill about to make landfall on the central Texas Gulf Coast

However, for people living in the path of Bill, it is not the wind but rather the potential for dangerous flash flooding that is the primary concern with this storm. Bill is forecast to bring as much as 10″ of rain over the next few days to parts of Texas, and upwards of 6″ for a wide swath of Oklahoma and Missouri. As you may recall, some of these areas were the scene of deadly flooding just a few weeks back, and the arrival of a rainmaker like Bill is most unwelcome for these areas that are still in the midst of recovering. Moisture from Bill will eventually work its way into our region, but in a much less intense way.

Forecast rainfall totals for TS Bill
Forecast rainfall totals for TS Bill