Summer-like warmth has given way to more seasonable temperatures for this time of the year. The return to normal temperatures will be accompanied by the possibility of rain. Later in the week, temperatures will climb back up again as we are forecast to be back in the warm sector of another approaching storm. This storm should bring some rain Friday and overnight into Saturday, resulting in what should be a decent weekend
Rest of today – mostly cloudy, temperatures in the upper-50s to around 60ºF. Increasing chance for showers later this evening, around 6PM when a line of showers accompanying a cold front is expected to hit the area. Overnight lows behind this front will be much cooler than last night, in the mid-40s.
High resolution rapid refresh simulated 1-km radar for 6PM tonight
Wednesday – should be a nice day with mostly sunny skies and temperatures in the upper-50s. Overnight lows will be cool, around 40ºF.
Thursday – cool start to the day results in high temperatures around the mid-50s with mostly sunny skies and increasing clouds. Overnight lows climbing into the upper-40s.
Weather Prediction Center surface forecast for 8AM Friday. Note that we’ll be in the warm sector of this storm for a good part of the day.
Friday – warmer, with high temperatures in the mid-50s. Chances for rain increasing later in the day with a cold front forecast to be approaching from the west. Overnight lows in the low-50s.
A cool start to the weekend should give way to a nice couple of days before another storm moves in to start next week. During this period, high temperatures will start well below normal, then rise above average before finally settling around average. Looking ahead, another storm system appears to impact the area late next week, bringing a colder weekend next week in its wake.
Rest of today – cool, cloudy with high temperatures only in the mid-40s. Increasing rain chances towards the evening and overnight hours. Rain should taper off overnight then we should see overnight lows stabilize in the low-40s as warm advection takes hold.
Saturday – clouds diminishing as the low responsible for the rain moves over the Atlantic to our south. High temperatures in the mid-60s, maybe a touch warmer if we see clouds break earlier than forecast. Overnight lows milder in the upper-40s.
Weather Prediction surface forecast for 8AM Sunday
Sunday – high pressure stays in control and gives us a pleasant, mild day with high temperatures in the low-60s. The high pressure and nice weather doesn’t stick around long though, with another storm system approaching during the overnight hours going into Monday. Overnight lows should hold around 50ºF as rain starts to fall.
Monday – despite clouds and rain sticking around, temperatures will surge to about 70°F with a warm front forecast to pass through.
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 April.
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 northwest occuring about 13% of the time.
Directions that are most and least common: Most common wind directions following due northwest are due south (10%), west-northwest (9%), and due northeast (8.75%). Least common wind directions are east-southeast (1.25%), due east (2.5%), and due southeast (2.75%).
Direction(s) most likely to produce the fastest winds: Winds from the northwest, west-northwest, and to some extent the northeast and east-northeast tend to produce the fastest winds.
Direction(s) least likely to produce the fastest winds: Winds from the east-southeast, due east, and south-southwest are least likely to produce the fastest winds.
Impacts of wind direction on local weather: Like March northwesterly winds during April are likely tied to the passage of cold fronts and coastal storms. Cold air advection from these winds will still be quite robust during the beginning of the month especially, as record lows for this month suggest. Winds from the northeast are still tied to backdoor cold fronts arriving from the Canadian Maritimes, bringing a moist, cool maritime polar air mass, or the advance of coastal Nor’easter type storms. During April, sea surface temperatures around NYC become markedly cooler than the air temperature as average highs continue climbing in response to more direct sun angle on longer spring days. On days approaching record warmth, in an overall environment of otherwise light winds, you could even see some sea breezes start forming along the coasts.
Maximum observed two-minute wind speed for the month: 48 knots (55 mph).
Temperature and Precipitation Averages/Records
Temperature units are in Fahrenheit and precipitation is in inches.
Worth Noting
April is the first month in the spring when record high temperatures exceed 90ºF. Record lows still routinely dip into the 20s during this month, reflecting the variability that spring can bring. The most recent record low was set in 2021, at 29ºF for 4/2. April also has the second highest single day precipitation record with 6.69″ falling on 4/15.
High pressure gives way to a be coastal storm that will sideswipe the area. Following this, we’ll see a brief warm up, but temperatures will cool off towards the end of the week. We have rain chances overnight into tomorrow and Friday night.
Rest of today – high temperatures around 50°F. Increasing clouds ahead of a coastal approaching from the south. Overnight, chance of rain with low temperatures around 40°F.
Weather Prediction Center surface forecast for 8AM Wednesday, depicting a coastal storm passing us to the southeast.
Wednesday – winds increasing to 15-20 mph in the afternoon. High temperatures warming into the low-60s be with clouds dissipating and winds shifting to the southwest. Overnight lows drop back into the low-40s behind the passage of a dry cold front. Winds will shift to a colder northwesterly direction.
Thursday – cooler with partly sunny skies and high temperatures in the mid-50s. Low temperatures colder in the upper-30s.
Friday – another low approaches from the southwest. High temperatures below average in the mid-40s, rain chances increase later in the day with the low pressure drawing closer. Rain chances continue into the overnight hours with lows in the low-40s.
We will have a warm though not too sunny start to the weekend. A solid chance for rain hits Sunday with the passage of a cold front. After that, temperatures will drop to below normal levels again. Looking ahead into next week, there should be a dry start to the week but a coastal storm may impact the area mid-week. There’s some outside chances for snow with this storm.
Rest of today – cloudy, with some chance of light rain though most rain should remain over interior. With southwesterly flow, despite clouds we should still reach into the upper-50s to 60°F. A cold front approaching from the west is forecast to stall out and acquire semi-stationary characteristics. Thanks to the continued influence of high pressure off to our east, we should stay mostly dry today. Overnight lows should be warm, near 50ºF.
Saturday – the warmth continues, with high temperatures forecast to reach well into the upper-60s though clouds will still linger around with the stationary front to our west. Overnight lows will be similar to tonight around 50ºF.
Weather Prediction Center surface forecast for 8AM Sunday
Sunday – the stalled frontal boundary finally picks up forward momentum and pushes through the area as a cold front. Ahead of it, temperatures will still be mild in the mid-50s. A line of showers is expected with this front during the day. Overnight lows behind this cold front will be considerably colder, in the low-30s.
Monday – dry, sunny weather, but with a chilly start to the day, temperatures are expected to only be in the upper-40s to near 50ºF, slightly below normal. Overnight lows are expected in the mid-30s.
This week’s weather features the prominent impact of a slow moving, strong area of high pressure over the region. That translates to calm, generally sunny conditions with a warm up towards the end of the week as the high slides east and we end up in a milder southwesterly flow on its western edge.
Rest of today – sunny but with cool northerly winds, we will remain below average with highs in the upper-40s and overnight lows in the low-30s
Wednesday – once again we have a cooling influence this time with northeast onshore winds that will keep temperatures below normal in the mid-40s with sunny conditions. Overnight lows again in the low-30s.
Weather Prediction Center surface forecast for 8PM Wednesday
Thursday – as the high pressure moves east of us, we see a shift in winds to the south. This should result in high temperatures right around average in the mid-50s. Should be comfortable spring weather for the Yankees home opener with a light wind blowing from right to left field. This is a welcome contrast from last year, when snow postponed the home opener! Overnight lows will be milder also in the mid-40s
Friday – the warm up continues with high temperatures kicking above normal in the low-60s. It appears the limiting factor for temperatures will be increasing clouds ahead of a cold front. Overnight lows in the upper-40s
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
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
A long duration Nor’easter slowly moves its way eastwards. Conditions improve during the second half of the weekend. A brief warmup to above average temperatures takes place. This doesn’t last, with another cold front passing through to start next week. Tomorrow, keep an eye out on the skies for a possible glimpse at the aurora borealis, typically not visible at these latitudes.
Rest of today – chance for rain shower diminishing as the center of a slow moving Nor’easter continues to progress northeast. High temperatures reaching around 50ºF. Winds will increase on the backside of this departing low overnight. Winds will shift towards the northwest as well, bringing in colder air and overnight lows in the mid-30s.
GOES East satellite loop of the storm system affecting the NortheastOcean Prediction Center surface analysis for the Atlantic Basin. A strong blocking high is inhibiting the forward progress of the Nor’easter impacting our area. This is leading to a long duration coastal flooding and wind event.
Saturday – decreasing clouds as the low above continues progressing northeast slowly. Winds will increase as this low continues to deepen and the pressure gradient builds between it and and area of high pressure further west. Steady winds in the 20-25 mph range with gusts as high as 40 mph are forecast. High temperatures will be a bit below normal as a result in the upper-40s. Overnight lows will be cold, in the mid-30s with clear skies.
Weather Prediction Center surface forecast for 8AM Sunday, still showing a tight pressure gradient between a high over the Ohio Valley and the departing Nor’easter
Sunday – temperatures rebound into the mid-50s as an area of high pressure builds and slides off to our southeast, and winds turn towards the southwest bringing in warmer air. Sunny skies – this will be the best day of the weekend.
Monday – another cold front approaches from the west and brings a possibility for rain. Temperatures ahead of this front should reach into the low-50s. Behind this, we’ll get another shot of cold air, with temperatures dropping overnight into the low-30s.
Northern Lights Possibly Visible from NYC
On Tuesday, The Space Weather Prediction Center (it exists!) detected a large Coronal Mass Ejection (CME) associated with a potent solar flare. As a result, they have issued a moderate geomagnetic storm watch for Saturday, March 23. Of note, the belt where the charged particles from this CME would impact the Earth’s upper atmosphere and result in an aurora quite a bit further south than where the northern lights are typically visible. In fact, they may even be visible from NYC, although it may be hard to see them due to light pollution.
Much above average warmth last Friday resulted in a spectacular light show from passing thunderstorms. In the wake of this, temperatures have dropped into a below average range, considerably cooler than this weekend. There will be a warm up later in the week though, along with some rain chances.
Rest of today – mostly sunny with high pressure in control. High temperatures in the mid-40s, overnight lows dropping into the mid-30s.
Tuesday – not too much of a difference between these two days. High pressure remains in control. High temperatures maybe a little warmer in the upper-40s, overnight lows again in the mid-30s.
Weather Prediction Center surface forecast for 8AM Wednesday
Wednesday – as high pressure shifts eastward, we should see a shift in winds to the west, allowing temperatures to warm into the low-50s. Overnight lows around 40°F.
Thursday – chance for showers with a frontal boundary moving through. High temperatures in the low-50s with mostly cloudy skies. Lows in the low-40s.
This weekend will see a warm start but then a cool down into the below normal range going into next week. A rumble of thunder and showers will precede this cool down. Weather looks pleasant for St. Patrick’s Day festivities and the NYC Half Marathon this weekend.
Rest of today – mostly cloudy with some breaks of sun after a warm front passes over shortly and we sit in the warm sector of the same storm that tore through the central US earlier this week. As the trailing cold front pulls through this evening, it could provide enough lift for some additional showers and possibly a couple thunderstorms. High temperatures will be above average in the low-60s, mid-60s if some sun breaks through while we’re in the warm sector. Overnight lows behind the cold front should be in the low-40s.
Weather Prediction Center surface forecast for 8PM Friday
Saturday – bright, sunny day with high pressure building behind the cold front. Temperatures cooler, around 50°F. Overnight lows much cooler in the low-30s.
Sunday – cold start to the NYC Half Marathon in the low-30s but high temperatures will end up in the mid-40s with lots of sun. Overnight lows again around the freezing mark
Monday – increasing clouds with a possibility for some precipitation but chances are too low now to call. Highs in the mid-40s and overnight lows back down in the low-30s again.
