All posts by Lei Zhao

Hurricane Irma Special Update – Sep 7, 2017

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This is one of an upcoming series of special posts dedicated to Hurricane Irma. I’m hoping these posts will keep those of you who are either in areas at risk or have friends and family there informed and prepared as this historic storm bears down on the US mainland.

Current Situation

Hurricane Irma remains an impressive Category 5 storm packing sustained wind speeds of 175 mph. It is nearing the Turks and Caicos Islands as of this time.

Headlines

  • The threat Irma poses to South Florida as a strong Category 4 storm continues to increase
  • There is a risk to the Georgia and South Carolina Coasts. This risk would increase if there’s eastward movement of the storm track, as was the case in previous track forecasts.
  • Major impacts are expected to the Turks and Caicos and Bahamas archipelagos
  • The threat to the northern coast of Cuba remains high. Hurricane watches have been upgraded to warnings.
  • This is a large hurricane – the larger the size of the storm, the larger the storm surge it can generate. Even if the eye of the storm misses Florida to the east, the entire state could still feel the impacts of tropical storm and hurricane force winds.

Forecast Track

Here is the National Hurricane Center’s latest official forecast with a 5-day cone of uncertainty reflecting the spread in forecast models. Models have been wavering between a more westerly and easterly track in the past 24 hours which would have big implications (see below).

Here are some actual forecast model outputs on the storm’s track.

 

GFS model run showing Irma very close to or making landfall on the Miami area on Sunday at 8AM

 

Forecast Intensity

Unless the core of the storm interacts with the high terrain of Cuba by making landfall on it, it is unlikely that Irma would weaken significantly.

Wind shear is expected to remain low at the mid-levels, which means basically zero disruption to the core of the storm. Sea surface temperatures are very warm in the Florida Straits and Bahamas. This will support the storm maintaining itself as a very powerful hurricane.

Irma is expected to approach South Florida as a dangerous Category 4 storm (sustained winds over 130 mph). Even with some interaction with Florida, Georgia and South Carolina could still expect a strong Category 2 (sustained winds > 95 mph) or a Category 3 (sustained winds > 115 mph).

 

Uncertainties

The critical component of forecast track uncertainty is the timing and degree of influence a mid-level trough (the dip in that solid black line in the image below) on initiating Irma to begin a turn to the north as it rounds the western periphery of the Bermuda high that has been steering it thus far. The effect of a mid-level trough is both to weaken the Bermuda high and also to exert a pull on Irma to the north.

 

The timing of Irma’s northward turn is significant as an earlier turn would result in a more easterly track, and a later turn would result in a more westerly track. A small deviation either way could either spare an area from a direct hit by the devastating eye of the storm or bring it right into the eye.

  • A track to the east that takes the center of the storm away from South Florida would result in a stronger impact on the Georgia/South Carolina coasts
  • A track to the west would reduce the possible dangers to Georgia and South Carolina but increase the threat to the entire Florida Peninsula. This would still result in serious impacts to South Florida.
  • Another factor to consider is that landfall on Cuba and any significant interaction of the core of the storm with the high mountains of Cuba would result in a weaker storm affecting Florida and other US locales

 

Irma’s Impacts Thus Far

Overnight into today, Hurricane Irma made landfall on several small Leeward Islands including Barbuda and Saint-Martin/Sint-Maarten. These islands took a direct hit from the eyewall of Irma, which packed sustained winds of 185 mph. This resulted in catastrophic damage to Barbuda that the prime minister described as rendering the island barely habitable. Below, you can watch some footage captured by a camera at Princess Juliana International Airport located in Sint-Maarten, the Dutch side of Saint Martin as the eyewall impacted that location.

As on Barbuda, scenes of widespread damage were to be found on Sint-Maarten as well. Here’s an infrared satellite image of Irma as its eye swallowed Anguilla and Saint-Martin/Sint-Maarten last night:

Hurricane Irma has smashed an all-time record for longest duration of winds at 185 mph in the satellite era (1970s or so onward) with these winds lasting for 36 hours. This is truly incredible considering that the strongest tropical cyclones are typically found in the Western Pacific where these storms have ample time over warm water to grow.

NYC Weather Update and Hurricane Irma – Sep 4, 2017

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The unofficial end of summer does indeed bring us a last gasp of summery weather. A cold front passing through mid-week brings rain and signals a return to more fall-like conditions. Later in the week, we will see high temperatures 5°F below normal. Turning towards the tropics, the risk Irma poses to our region is diminishing, but it now appears Irma will be a threat to Florida.

Rest of today – clear, with ideal conditions for outdoor activities of all kinds. High temperatures in the low-80s.

Tuesday – highs in the low-mid 80s as warm air surges ahead of an advancing cold front. Mostly sunny with increasing clouds late in the day. Some possibility for a spot shower or thunderstorm in the afternoon.

Wednesday – thunderstorms are possible overnight Tuesday as the leading edge of the cold front advances through the area. More rain is expected to ride along the frontal boundary after it passes through, bringing periods of showers throughout the day. High temperatures will be much cooler in the mid-70s with the clouds and rain.

Thursday – mostly cloudy to start with a chance for lingering rain. High temperatures will be cool again in the low-70s.

Friday – mostly sunny skies, much improved conditions as high pressure takes hold. Cool, with high temperatures in the low-70s.

 

Hurricane Irma an Increasing Threat to Florida

Over the weekend, Irma has been fluctuating in strengthen as it has negotiated marginal conditions for strengthening (mostly the influence of some dry air at upper levels). The National Hurricane Center still forecasts Irma to attain Category 4 strength at some point later this week (130 mph sustained winds or higher) as it encounters more favorable conditions for strengthening, and maintain at least Category 3 strengthen (sustained winds > 115 mph) throughout the forecast period.

The track forecast for Irma has continuously shifted west and south over the weekend due to the influence of an area of high pressure over the Atlantic now, and a faster forecast for the passage of the cold front mentioned above. This frontal boundary lifting out of the East Coast at a faster rate than in prior forecasts would mean that it does not influence Irma to make a turn to the north-northwest and threaten the East Coast. This has two consequences: 1) The chance for Irma to make landfall up the East Coast is diminishing, 2) On the other hand, the risk to Florida is increasing.

This run of the GFS forecast model suggests Irma making landfall on South Florida as a powerful Category 3 hurricane in one week’s time.
A “spaghetti” plot of multiple model runs of GEFS, one of the forecast models that forecasters are using to analyze Irma.

It is important to note that with a week to go before Irma nears the US mainland, there could still be room for changes to the track and intensity forecasts. The National Hurricane Center specifically cautions against drawing premature conclusions about the storm’s impact on the rest of the US, while singling out Florida as an area of concern. More updates to come as we continue to watch the development of what could be a very dangerous storm.

NYC Labor Day Weekend Weather, Eyes on Irma – Sep 1, 2017

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It will definitely feel like the end of summer this weekend as temperatures will be much below average for this time of the year. The remnants of Harvey are also likely to put a damper on weekend activities Saturday night through a decent chunk of Sunday. Labor Day Monday itself looks like a gem. In the long term, I’m keeping tabs up Hurricane Irma, which worries me with its potential to affect the East Coast.

Rest of today – cool, with a Canadian high pressure center to our north-northwest, we’ll feel a refreshing north wind that will diminish through the day. High temperatures are only forecast to hit 70ºF or so even with sunny skies, 10ºF+ below normal for this time of year.

Saturday – temperatures remain cool in the uppper-60s with an easterly onshore flow ahead of an approaching warm front associated with the remnants of Harvey. Overrunning clouds will move in before rain chances build up overnight.

Sunday – rain lingers into the day on Sunday before ending by the afternoon. Mostly cloudy with temperatures in the mid-70s as we get some warmer return flow behind the storm with high pressure setting up to our southwest.

Monday – the warming pattering continues with highs returning to around normal in the low-80s with sunny skies. This is the best day for your holiday weekend grilling, and should be excellent viewing conditions for the annual West Indian Day Parade and carnival.

 

Hurricane Irma – possible threat to the East Coast?

We’ve entered the peak of the hurricane season and right on the toes of Harvey we have Hurricane Irma which put on an impressive display of strengthening the last couple days wen it went from a tropical storm to Category 3 major hurricane. It’s weakened a slight bit but conditions are still favorable for it re-strengthen into a powerful Category 3 of 4 storm before making an approach on the Lesser Antilles.

What is concerning to me is the storm is forecast to take a jog to the southwest over the weekend. The further south and west this storm gets before it starts the process of curving back out to sea at a higher latitude, the greater the chance that it could impact the East Coast of the US. There is still a lot of time so things could definitely change, but it is worth noting that current forecasts favor a more southerly track, enhancing the risk to us. I’ve seen GFS model runs show the storm make direct landfall on the Mid-Atlantic and Northeast. As of this morning, the GFS backed off of this type of scenario. It does bear watching though.

NYC Weather Update – Aug 28, 2017

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Nice weather from the weekend continues today. Chance for rain on Tuesday. Temperatures remain below normal through the week except Thursday. Labor Day weekend looks to start off like autumn.

Rest of today – clouds this morning expected to dissipate somewhat. Below normal temperatures with highs in the upper-70s.

Tuesday – a disturbance off the coast of northeast Florida has the potential to develop into Tropical Storm Irma. Regardless of whether the storm successfully undergoes tropical cyclogenesis, it is still anticipated to bring us some tangible weather impacts. This would be in the form of some rain especially later in the day as it makes a transition to an extra-tropical storm.

Easterly onshore winds from this storm to our south will suppress high temperatures in the low-70s and give us a mostly cloudy day.

Wednesday – unlike Tropical Storm Harvey, the storm above will accelerate quickly out to the Atlantic, so Wednesday should turn out to be a pretty decent day with mostly sunny skies and temperatures rebounding back to the upper-70s.

Thursday – a cold front will pass through the area during the day and could trigger a few scattered thunderstorms. Warmer air ahead of the cold front should give us about average high temperatures in the low-80s.

 

Peak Hurricane Season

We’re on the cusp of the traditional peak of the Atlantic Hurricane season, which typically begins around late August and lasts through till late September. This period typically sees the highest oceanic surface temperatures (due to the specific heat of water being relatively high, there’s a lag in time between peak solar heating of summer and actual peak ocean temperatures), which in ups the potential for tropical cyclone development.

Not surprisingly, we’ve got Harvey still devastating the Texas coast, about to re-emerge over open water before making a second landfall later this week. We’ve also got a possible tropical cyclone off of the Southeast coast and another tropical wave moving offshore of Africa that could develop into a tropical storm as it moves west. A lot of activity to monitor, hoping that none of it comes our way!

NYC Weekend Weather + Note on Harvey – Aug 25, 2017

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I’ve returned from Europe (missed the eclipse though!) to a very pleasant stretch of calm weather and slightly below normal temperatures. Surface high pressure to our northwest over Ontario will continue to bring us cool, dry Canadian air that evokes a more fall-like feel.

Rest of today – just about normal temperatures with highs around 80°F, skies have cleared up nicely and we should have spectacular weather for the start of the weekend.

Saturday – high pressure remains in control, and gives us another pristine day of slightly below normal temperatures in the upper-70s but lots of sun.

Sunday – basically a clone of Saturday, high temperatures in the upper-70s, lots of sun.

Monday – more of the same with temperatures again in the upper-70s, maybe a few more clouds, but who can complain especially when you consider the next section.

 

Hurricane Harvey a Major Threat to the Texas Coast

It’s worth mentioning here that we have a very dangerous situation developing on the Texas coast today and over the course of the next few days with Hurricane Harvey. If you have friends or family in this area, it’s not a bad idea just to try and check in with them.

GOES 16 visible satellite image of Harvey showing impressive size, distinctive eye, decent symmetrical outflow except on the side already beginning to interact with land.

Harvey originally formed over the eastern Caribbean, dissipated approaching the Yucatan, and then redeveloped as it emerged over the Bay of Campeche. Favorable conditions have allowed Harvey to strengthen quickly into a Category 2 storm, and it’s forecast to continue strengthening to Category 3 before landfall.

This would make it the first major hurricane to make landfall on the US mainland in nearly 12 years. The biggest concern with Harvey is that most forecast models have the storm stalling out after landfall, and possibly looping back out to the Gulf and making a second landfall mid-week next week in eastern Texas, still retaining tropical storm strength. Two areas of upper-level high pressure will essentially be trapping Harvey in place.

The slowing forward motion of the storm means that tropical storm and hurricane force winds will rage for many hours. The longer the winds churn up the waters of the gulf, the bigger the life-threatening storm surge along the coast. Peak storm surge of 6-12′ is forecast. That’s without waves on top. For reference, Sandy brought a peak storm surge of 14′ to The Battery. That’s well above the first, and well into the second story of most homes. On top of that, rainfall totals measuring 2-3′ are possible, which would cause widespread inland flooding.

NYC Weather Update – Aug 7, 2017

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A pleasant Sunday gives way to a wet and cool start to the week. High pressure builds in as Monday’s storm system moves out of the area. The rest of the week, we’ll see below average temperatures, but mostly sunny conditions along with a more comfortable, drier airmass. This will be my last update for a couple of weeks as I’ll be traveling to Europe – I’ll miss out on the solar eclipse happening on August 21st, which I’ll give some details on in this post.

Rest of today – a low pressure center tracking near or over Long Island during the day today will bring multiple rounds of rain, which at times could be heavy. Conditions will deteriorate during the morning, and rains should pick up in the afternoon. A brief pause may occur before another round of heavy rain during the evening and overnight hours. A flash flood watch is in effect due to the possibility of upwards of 2″ of rain falling perhaps in short intervals. Temperatures will be cool with southeast winds off the ocean and clouds keeping things only in the low-mid 70s.

Tuesday – as this storm system pulls away, winds shift to the northwest and high pressure begins to build in. Tuesday should see partly sunny skies clearing up and high temperatures around 80°F.

Wednesday – nice crisp day on tap with high temperatures around 80°F again and lots of sun as high pressure remains in control.

Thursday – a notch warmer with high temperatures in the low-80s and mostly sunny skies.

 

Total Solar Eclipse of August 21st, 2017

This much anticipated astronomical event is approaching in 2 weeks time. The last total solar eclipse that would have been highly visible from a large portion of the continental United States dates back to March 7, 1970. This greatest magnitude of this eclipse traveled nearly directly over all the major cities of the Eastern Seaboard.

Path of the total solar eclipse of March 7, 1970

Unfortunately, this time around, we won’t be quite as lucky in New York City, but we’re still expecting around a .75 magnitude total solar eclipse peaking around 2:45PM on August 21st.  Regardless, it will be an impressive sight to behold as 3/4 of the sun will be blocked out by the moon transiting directly in front of it from our viewpoint. Even with cloudy skies, you should still notice an appreciable change in lighting during this eclipse event. Hope it stays sunny though!

NYC Weekend Weather – Aug 4, 2017

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A hot week transitions into a weekend that will see the end of the heat and humidity for at least half of next week and maybe longer. Rain and thunderstorms dot the forecast except appropriately Sunday.

Rest of today – partly sunny with high temperatures in the mid-80s. The rain and thunderstorms this morning give way to a dry day otherwise.

Saturday – a warm front moves through overnight into the morning with a cold front following right on its heels. This will bring a period thunderstorms producing heavy rain at times. Marginally favorable atmospheric conditions could spawn a few strong storms. Clouds clear up in the afternoon and highs are expected to reach normal levels in the mid-80s.

Sunday – cooler, drier air moves in behind the cold front Saturday. High pressure builds to the south and west and moves south sending cooler Canadian air around its periphery towards us. High temperatures will be comfortable around 80°F with lots of sun.

Monday – a weak disturbance brings rain and cooler temperatures, well below average only in the mid-upper 70s.

Trouble in the Tropics?

A vigorous tropical wave has spun up off the west African coast and Cabo Verde. Storms originating from this region have historically been some of the most powerful and damaging, but that’s if they can sustain the transit across the Atlantic. The National Hurricane Center has this wave at a 50% of forming into a tropical depression or storm in 2 days, and 80% chance in 5 days. It’s worrying that it’s starting to get picked up on long-term GFS model runs taking a swipe at the US East Coast as a strong tropical cyclone, however, this far out, it’s difficult to say which one of many scenarios could play out. It does bear monitoring though.

GFS for Wednesday 8/16, with the tropical system in the picture right off the East Coast of the US.

NYC Weather Update – Aug 1, 2017

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We enter the month of August with much more appropriate, summer weather and temperatures to match. High pressure over the eastern half of the country dictates the weather this week, with plenty of sun and temperatures finally in the normal to above normal range in the mid-upper 80s. Humidity increases and results in daily afternoon chances for showers and thunderstorms.

Rest of today – sunny with high temperatures in the mid-80s.

Tuesday – warmer, sunny with high temperatures in the upper-80s to near 90°F.

Wednesday – similar picture to Tuesday with highs in the upper-80s to around 90 °F, chance for an afternoon shower or thunderstorm.

Thursday – cooler with temperatures back in the mid-80s range and another chance for thunderstorms in the afternoon.

NYC Weekend Weather – Jul 28, 2017

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After a couple days of average temperatures, this weekend sees a return to cool temperatures with a wet start to it all. Conditions improve Sunday, and high pressure builds but temperatures remain below normal until later next week.

Rest of today – increasing clouds as a coastal low begins to form off the Mid-Atlantic. Warm with high temperatures right around normal in the low-mid 80s. Rain should hold off until the overnight hours.

High resolution rapid refresh model runs don’t show significant rainfall until around 2AM EDT Saturday

Saturday – an unpleasant, raw, windy, rainy day more reminiscent of autumn or spring than late July. As the coastal low moves closer to us along a stalled frontal boundary, it will bring chances for moderate to heavy rain along with a stiff northeast wind around 25 mph. As a result, temperatures will be surpressed in the mid-70s. Rain chances taper off during the day as the low moves east.

Sunday – much nicer with plenty of sun and temperatures rebounding to around 80°F. Still will have a cooling influence of the weakening northeast winds.

Monday – high pressure builds and yields another decent day with high temperatures around 80°F, possibly higher with more sun.

NYC Weather Update – Jul 24, 2017

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This past weekend, we saw a heatwave broken by several rounds of moderate to heavy rain associated with a couple frontal systems. In their wake, we start this week with temperatures below seasonal averages. This cooler airmass will dry out midweek and give us very comfortable average temperatures in the low-80s.

Rest of today – one more round of moderate to heavy rain pushing through now, then expect a break from the rain during the remainder of the day before another chance for showers later this evening and into the overnight hours, around 8-10PM. Cool, with am easterly onshore flow. High temperatures in the upper-70s.

Tuesday – high pressure begins to build but may not be sufficiently strong to completely remove the chance for showers especially early. Temperatures remain cool in the mid-70s again with a northeasterly onshore influence and cloudy skies.

Wednesday – warmer and sunny finally with high pressure in control, highs will rise into the low-80s.

Thursday – warmer still and into average high temperatures with highs in the mid-80s, but the tradeoff is increasing clouds.