observations, weather

Vertical atmospheric mixing – Part 2 (H. Michael Mogil, CCM, CBM, DMS)

A few weeks ago, I posted an article about vertical atmospheric mixing. The article focused on a single day (Oct. 10, 2016) in Portland, ME. In the article, I looked at both the variability of winds during a 24-hour period (day versus night) and also examined atmospheric soundings.

fig001-sfc-wx-maps-161027-29Today, I’d like to address a multi-day wind event in Florida, keying specifically on where I live, Naples (southwest coast). For the past four days, our area has been under a persistent east to northeast wind flow. A clockwise wind pattern around a large high-pressure system along the East coast (Fig. 1) has controlled this near-ground wind flow. For purposes of this article, I will leave out the sounding component, instead looking only at the day to night wind speed variability.

fig002-meteogram-apf-161026Note, please that both the Maine weather scenario and the one being explained here came to light by OBSERVING the weather that was taking place. Observation is a key part of the scientific method…and in my opinion, perhaps the most important.
fig003-meteogram-apf-161027 Figs. 2, 3, 4 and 5 show the daily (8:00 p.m. E.D.T to 7:00 p.m. E.D.T) meteograms for Naples, FL (KAPF airport code) for Oct. 26 – 29, 2016. Fig. 6 summarizes the average wind speed for the day and night periods (hourly data only, 8:00 p.m. E.D.T. – 7:00 a.m. E.D.T. and 8:00 a.m. E.D.T. –

fig004-meteogram-apf-161028 7:00 p.m. E.D.T.) for the four-day period. Fig. 6 also shows the average gusts (basically, the peak wind speed during the observational period; to have a gust, wind speed variability must be greater than 10 knots or 11.5 miles per hour) for the two twelve-hour periods. It is easy to see just how strongly the wind speed and gustiness changed between the day-night periods.

fig005-meteogram-apf-161029 Simply stated, when all else is equal, wind speeds and gustiness during daylight hours will be greater than adjacent nighttime periods.

 

 

 

 

fig006-wind-analysis-apf-161026-161029And, with the weather pattern across south Florida remaining in place, this “daytime windiness – nighttime calmer” wind pattern should continue, at least into mid-week.

© 2016 H. Michael Mogil

Originally posted 10/31/16

weather

Mostly a good weather forecast (H. Michael Mogil, CCM, CBM, DMS)

The following is combined forecast and weather-torial. It reflects my opinions only and not those of the GWCC web site, its directors and/or its correspondent base.

During severe weather situations, the media (and the NWS) are quick to note the number of people (in the 10’s of millions) who are, “under the gun.” Yet, in some small-scale situations, the number affected may actually be quite small. In other cases (larger-scale storm systems), large numbers of people may be under a weather watch, but significantly lesser numbers are actually affected by the weather. Personally, I think this framework is hype. The bigger the danger numbers presented, the bigger the ratings. This only fosters a “cry-wolf” mentality going forward. Further, our job as meteorologists should be to cover the weather and ensure timely and useful information is in the hands of the public.

fig001-upper-level-winds-161029So, it is with great pleasure that I announce the following. For the upcoming week, some 200 million people across the U.S. will be affected by mostly good weather! A zonal (west-to-east) and northwesterly upper level wind flow (associated with a broad upper level ridge [Fig. 1] across the western states) will keep much of the U.S. under mostly sunny skies, low relative humidity readings and seasonally pleasant temperatures.

fig002-7-day-rainfall-thru-161029The main exceptions will involve a lingering storm system across the northeast and parts of the Great Lake and a strong onshore flow across the northwest U.S. In these places, cloudiness will be more extensive and prevalent and rainfall will be heavier (Fig. 2).

Of course, the good weather comes with some bad news. Drought areas in the west and southeast regions will stay locked in drought; given the dry conditions, there is a growing risk of forest and grassland fires, as well.

Still, most can’t argue against really pleasant autumnal weather. Here is southwest Florida, low temperature readings in the 50’s, like those experienced this Sunday morning, are to be cherished!

© 2016 H. Michael Mogil

Originally posted 10/23/16

biology, geography, learning, oceanography, weather

Red tide still affecting many southwest Florida beaches (H. Michael Mogil, CCM, CBM, DMS)

For weeks, a “red tide” (such tides are also referred to as a “harmful algal bloom” or HAB) has affected many beaches from Lee County, FL northward. With the departure of Hurricane Matthew a little over a week ago, the HAB was pushed southward and eastward, finally reaching beaches in Collier County. A day earlier (Fri., Oct. 6, 2016), news reports from Sarasota, FL indicated that with increasing winds and winds blowing from land to water (the approach of Matthew), the tide in its area would likely lessen. Unfortunately, the tide had to go somewhere. On Sat., Oct. 7, 2016, the HAB’s smelly signature arrived in Naples, FL. The tide has since returned to Sarasota area beaches, as well.

According to Florida’s Fish and Wildlife Conservation Commission, a “red tide is a naturally-occurring microscopic alga that has been documented along Florida’s Gulf Coast since the 1840’s and occurs nearly every year. Blooms, or higher-than-normal concentrations, of the Florida red tide alga, Karenia brevis, frequently occur in the Gulf of Mexico at this time of year (late summer or early fall). Red tide begins in the Gulf of Mexico 10 to 40 miles offshore and can be transported in (to) shore by winds and currents.”

fig001-san-diego-area-algal-bloom-imageAs the name “red tide” suggests, this bloom of algae often turns the water red (Fig. 1).

A HAB has two potential components. First, according to NOAA’s National Ocean Service (NOS), are the harmful toxins that some (not all) algal blooms create. Florida’s “red tide” bloom is of the type that can kill fish and make shellfish dangerous to eat. These same toxins may also make the surrounding air difficult to breathe. Both of these can have local economic impacts (fishing and tourism).

Another way the algal bloom (even without the presence of harmful toxins) can harm marine life involves the natural end-of-life of the bloom. According to NOS, “…when masses of algae die and decompose, the decaying process can deplete oxygen in the water, causing the water to become so low in oxygen that animals either leave the area or die.”

fig002-dead-fish-at-vanderbilt-beach-naples-161007Either way, with onshore winds and/or an ocean current with a coastward component, there is the potential for dead fish to wash up on the beach (as I personally witnessed 10 days ago on a north Naples beach). The presence of hundreds to tens of thousands of dead fish makes a beach a very unattractive and very odiferous place to visit (Fig. 2). This setting can easily ruin vacations and impact a local area’s tourism industry.

Local agencies and volunteers often work quickly to clean up the dead fish. However, as long as the tide sits nearby, fish deposition on the shore often continues.

fig003-sfl-watch-warning-map-161017-0630amedtCurrently, the National Weather Service (NWS) offices in Miami and Tampa Bay have posted “beach hazards statements” advising of the HAB’s potential human impacts through this Monday evening (Oct. 17, 2016) along many southwest Florida beaches (including those in Collier, Pineallis, Sarasota and Manatee counties). See Fig. 3 for affected areas in southwest Florida.  These statements note that, the red tide affecting the area may cause, “…possible respiratory irritation in some coastal areas. The irritation can include coughing, sneezing, and/or tearing eyes.” The statements further note that, “…people with respiratory conditions such as asthma, emphysema and other pulmonary diseases may be more sensitive (to these conditions).” The statements also urge people to check out current “red tide” conditions at the following web sites:

http://tidesandcurrents,noaa.gov/hab

http://mote.org/beaches

http://myfwc.com/redtidestatus and consider visiting nearby unaffected beaches.

For health information, people should check with their physician, as appropriate. People can also get medical information at the floridahealth.gov web site or by calling the Poison Control Center at 1-800-222-1222

For links to “red tide” conditions across other coastal states, visit NOAA’s “red tide” web site.

© 2016 H. Michael Mogil

Originally posted 10/17/16

weather

Extremely dangerous Nicole aims for Bermuda (H. Michael Mogil, CCM, CBM, DMS)

fig001-goes-e-eir-rainbow-161013-0745zGiven her size and strength, Category 4 (EXTREMELY DANGEROUS) Hurricane Nicole is likely to bring major impacts to Bermuda today (Oct. 13, 2016). As of 5:00 a.m. Atlantic Standard Time (A.S.T.) or 5:00 a.m. E.D.T., Nicole was located about 100 miles to the southwest of the tiny island Nation of Bermuda and was moving to the north-northeast at 15 miles per hour. According to the National Hurricane Center (NHC), Nicole is expected to be at major hurricane strength when it moves near Bermuda later today. It is easy to see how close Nicole is to Bermuda in this enhanced overnight infrared GOES satellite image (Fig. 1).

NHC’s early morning advisory notes that Nicole is a large tropical cyclone. Hurricane-force winds extend outward up to 65 miles from the center and tropical-storm-force winds extend outward up to 175 miles. With the storm already so close to Bermuda, it is no surprise that Bermuda International Airport (KTXF) has recently reported sustained winds of 43 miles per hour with a gust to 62 miles per hour.

The last Category 3 storm to strike Bermuda was Fabian on Sept. 5, 2003 (with sustained winds of 120 miles per hour and gusts to 164 miles per hour). Prior to Fabian, the most destructive storm to strike the island was back in 1926 (prior to the start of storm naming).

In addition to hurricane force winds, NHC forecasters are concerned about the following hazards for Bermuda:

  • a dangerous storm surge will raise water levels by as much as 6 to 8 feet above normal tide levels in Bermuda. The surge will be accompanied by large and destructive waves.
  • total rainfall accumulations of 5 to 8 inches through this evening.
  • swells associated with Nicole will create dangerous surf conditions and rip currents.
  • isolated tornadoes are possible on Bermuda.

Swells will also spread to the U.S. East Coast during the next few days, creating similar coastal risks of dangerous surf conditions and rip currents. Some beach erosion is also possible. With a full moon slated for Oct. 16, 2016, tides will be higher than at other times during the month. This could add to coastal flooding risks.

© 2016 H. Michael Mogil

Originally posted 10/13/16

weather

Vertical atmospheric mixing (H. Michael Mogil, CCM, CBM, DMS)

Most of us have seen what happens when a pot of water, sitting on a heated stove top, starts to boil. Bubbles form on the bottom of the water, and when they get big enough, they start to rise. But, if all the bubbles were to rise without any water replacement, there would be a hole in the bottom of the water. Hence, water from the top must come down to take its place. This is called convection (upward and downward movement of fluids) and involves mixing the water (warmer water rises and cooler water sinks to take its place). When the water boils vigorously, it is easy to see the mixing.

This process also happens in many atmospheric and oceanic settings, although not as quickly and not as visible. For the purposes of this article, I’ll concentrate on daytime heating of the ground (which is akin to heating the bottom of the pot). Hence, as sunlight heats the ground, rising “bubbles” of air (referred to as air parcels, in weather circles) develop. As this happens, air from above must come down to take the place of rising air parcels.

In the pot, horizontal motions were not present. In the atmosphere there are horizontal air movements (i.e., winds). And, typically, what happens at night is that the winds several thousand feet above ground are decoupled from winds nearer the ground. As a result, winds above ground level may be blowing quite strongly, while near the ground, winds are much lighter to calm.

As daytime heating, convection and mixing develop, higher wind speed air from above the ground is brought down to the ground. This mixing process increases winds near the ground and reduces winds above the ground. It also acts to equalize air temperatures in the mixed layer.

fig001-meteogram-kpwm-161010Fig. 1 (a meteogram for Portland, ME – PWM) is a prime example of the effects of this process. In the wake of Matthew moving away from the U.S. mainland and the passage of a cold front, winds at Portland, ME were relatively light before sunrise on Oct. 10, 2016. Once sunlight kicked in, winds and wind gusts picked up dramatically. As sunset occurred, winds dropped off, just as quickly and dramatically.

Not shown are two soundings (atmospheric balloon probes) from Portland, ME from Oct. 10, 2016. In the morning sounding, winds a few thousand feet above the ground were blowing at about 35 miles per hour, while winds near the ground were blowing between 10 and 15 miles per hour. At around six thousand feet above ground, winds were blowing at 55 miles per hour!

By early evening, winds had mixed throughout the lowest 10 thousand feet. Except for near the ground (which had already decoupled from the winds higher up in the atmosphere), winds were blowing a more or less uniform 30 miles an hour.

This effect happens on many days across the Nation (and around the world), especially during the chillier months of the year. Sometimes, however, with moving weather systems and other factors, it’s just harder to see what is happening.

The next time you experience a windy day and a calm morning and/or evening, think about vertical mixing. You can see what a nearby sounding looks like by visiting the Plymouth State University web site or another reliable weather web site that posts real-time sounding graphics.

© 2016 H. Michael Mogil

Originally posted 10/12/16

weather

Scheduling the arrival of Matthew’s winds (H. Michael Mogil, CCM, CBM, DMS)

fig001-sfl-watch-warning-map-161006-1145amedtNational Weather Service (NWS) offices from Florida northward to the Carolinas have been publishing numerous “local action statements” and other information about Category 4 (Major Hurricane) Matthew (Fig. 1). Included are probabilities of various weather hazards, flooding maps, storm track maps and much more. Local media outlets, reliable weather bloggers, private sector weather providers and others are sharing this information. So, too, are we here at the Global Weather and Climate Center. Our bloggers / weather correspondents will also be trying to add the scientific underpinnings for some of the information.

A short while ago, the NWS Miami office provided it’s latest thinking on the timing of the onset of hurricane and tropical storm force winds across south Florida. Rob Molleda, the Warnings Coordination Meteorologist for the office, emphasized that, “these are on the earlier side and are for SUSTAINED (at least 1 minute in duration) winds. Gusts to tropical storm force (39 mph or greater) in periodic squalls will begin early this afternoon over east coast locations and over interior and western sections of South Florida starting mid-afternoon. These GUSTS are for short-duration winds, those not sustained for more than 1 minute.” This is important because some news media outlets use gusts to define the worst weather. Yet, “hurricane force wind gusts” do not mean that hurricane conditions occurred!

Period of sustained tropical storm force winds (39 mph or greater) for far south Florida locations (not including the Keys):

Palm Beach County: 3:00 p.m. Today – 8:00 a.m. Friday

Broward County: 3 PM Today – 3 AM Friday

Miami-Dade County: 3:00 p.m. Today – 1:00 a.m. Friday (most likely north and east/coastal sections)

Hendry/Glades/Interior Collier County/Lake Okeechobee: 8:00 p.m. Today – 8:00 a.m. Friday, ending earlier in Collier County

Coastal Collier County: no hurricane force winds are forecast. If storm tracks more to the west, timing of onset of hurricane force winds would be between 8:00 p.m. – 10:00 p.m. tonight, lasting through 5:00 a.m. Friday.

Period of sustained hurricane force winds (74 mph or greater):

Palm Beach County: 9:00 p.m. Tonight – 6:00 a.m. Friday

Broward County: none forecast, but potential from 9:00 p.m. Tonight – 3:00 a.m. Friday, if Matthew’s track shifts to the west.

© 2016 H. Michael Mogil

Originally posted 10/6/16

 

weather, weather safety/preparedness

Matthew heading for Florida… (H. Michael Mogil, CCM, CBM, DMS)

There’s an old expression about, “proximity.” It goes, “close, but no cigars.” That was clearly contrived in another era. However, in the case of Matthew, close may be close enough.

fig001-matthew-nhc-track-fcst-map-161005-8amedtThe latest National Hurricane Center’s (NHC) projected track for Matthew brings him very close to the Florida east coast near Jupiter Beach, FL by early Friday (Fig. 1). Given the size of the tropical force wind zone (sustained winds up to and including 73 miles per hour), which has been focused to within about 45 miles from the storm’s eye (with tropical storm force winds extending outward some 175 miles outward from the eye), many places in Florida will be very windy on Thursday and Friday. Locations closest to the east coast of Florida will be at the highest risk of hurricane force winds; many inland locales will experience tropical storm force winds.

fig002-sfl-watch-warning-map-161005-8amedtAs a result of Matthew’s closer approach to the east coast of Florida, hurricane and tropical storm watches and warnings have been posted for much of southern and eastern Florida (Fig. 2).

Don’t be misled by some TV meteorologists and news folks who prefer to focus on wind gusts. Wind gusts are not the measure of tropical storm or hurricane wind force conditions. They may be good for inciting excitement that the storm is stronger than it is, but…

The entire suite of hurricane dangers can be expected along the east coast of Florida. This includes high winds, torrential rains, coastal wave action, storm surge, beach erosion, local flooding and even a risk (albeit low) of tornadoes. Inland locations of south Florida, as far west as the north-south I75 corridor, can expect high winds. There will likely be a very significant rainfall gradient between coastal and inland locales, with the heaviest rainfall closer to the coast.

West coast Florida coastal areas can expect some rough surf and beach erosion.

Obviously, winds and waves over nearshore and offshore areas and Lake Okeechobee will make any water-based activities extremely dangerous.

In addition to state-declared states of emergency from Florida northward to the Carolinas, airlines have begun implementation of no-charge rebooking programs, especially for flights departing from east coast Florida airports. Note that some airlines will charge the current price of a ticket, not the price paid months ago (please read the fine print to be sure).

Florida Power and Light (FP & L), the state’s major energy supplier, has sent e-mail notices to its business customers advising them that FP &L was ready for the storm. No doubt, supermarket shelves will soon be stripped of toilet paper, milk, eggs, break and water. Hardware store will soon have no plywood for sale. And gas station lines have been reported as being long.

A safe rule, espoused by emergency management agencies, especially for hurricane warning areas, is to have a 3-day supply of water and non-refrigerated food on hand.

In some places along the southeast coast (particularly South Carolina) coastal evacuations are being ordered. This includes the state’s lane reversal evacuation plan to lessen gridlock. Under the plan, Interstate 26 will only allow traffic flow away from the coast. In other places, county evacuations are being urged, especially for low-lying coastal areas and/or sand bags are being provided by local government agencies.

As I have noted for the past several days, tropical cyclone forecast position errors grow with time. NHC has willingly shared its error values: around 175 miles at day 4 (96 hour forecast) and 230 miles at day 5 (120 hours forecast). Hence, Matthew could wind up being positioned anywhere within or near the “cone of uncertainty.”

With a storm, roughly paralleling the coast, even a slight shift is track can produce significant changes to expected weather and water conditions. One has only to think back to Hurricane Charley in 2004. For that event, a slight jog toward Florida’s west coast yielded a landfall just north of Fort Myers, rather the expected landfall 150-200 miles further north, near Tampa.

fig003-4-5-matthew-modle-forecasts-valid-161011-00z-8amedtLooking well into the future, where forecast errors continue to grow, Matthew has transitioned from a New England/eastern Canada landfall to one in which the storm was expected to race across the north Atlantic toward western Europe to the current scenario in which Matthew stays roughly in place off the southeast coast and returns to the Miami area later next week. This is all the result of changes in upper level wind forecasts (because upper level winds steer hurricanes). Figures 3 through 5 showcase a few of these long-range solutions (all valid for the same time – 8:00 a.m. E.D.T. on Oct. 11, 2016).

With this long-term solution scatter in mind, it’s best to key on the first five days of the forecast. Get ready if you are in a watch or warning area and stay tuned to reliable weather updates through the period of risk.

© 2016 H. Michael Mogil

Originally posted 10/5/16

weather

Matthew – a significant threat to the U.S. East Coast… (H. Michael Mogil, CCM, CBM, DMS)

This morning, while Matthew continues to pummel parts of the western Caribbean with high winds, high waves, heavy rainfall, mudslides and more, forecasters are becoming increasingly concerned about Matthew’s future. Matthew now poses a significant risk to much of the U.S. East Coast. Governors in several states have already declared states of emergency, allowing them mobilize resources more easily, should Matthew’s threat materialize.

fig001-matthew-sat-winds-161004-00z-8amedtAs computer models continue to show a more westward pathway for Matthew, satellite imagery and derived (satellite-based) upper level winds support the trend (Fig. 1). The upper level ridge to the north of Matthew was supposed to weaken and allow Matthew to move northward far enough offshore for the U.S. East Coast. Instead, the ridge has built westward and maintained its strength.

As a result, all eyes are now focused on potential storm impacts from Florida northward to New England and the Canadian Maritime provinces. Even if Matthew stays offshore, high waves, a persistent fetch of waters onshore, strong and gusty winds, and some areas of very heavy rainfall are likely. If landfall occurs, impacts could be far greater, especially in and near the landfall area.

Even the west coast of Florida isn’t immune from Matthew’s potential wrath. In addition to the risk of some heavy rainfall and gusty winds on land, gusty onshore winds on the west side of the storm could lead to high waves, beach erosion and some coastal flooding.

Right now, based on the Global Forecast System (GFS) model, it appears that parts of New England stand the greatest threat for a direct hit from Matthew. The GFS takes a re-strengthening storm directly onshore in Maine this coming weekend.

As always, note that forecast position errors grow with time. Errors are around 175 miles at day 4 (96 hour forecast) and 230 miles at day 5 (120 hours forecast).

Stay tuned to your local and national news media outlets and weather reports for the latest details concerning storm positioning, potential impacts and emergency notifications. Visit the Global Weather and Climate Center, too. Our correspondents will be posting the latest information and explanations about the storm and about hurricanes, in general. We’ll also be providing information details that may not appear in other media outlets (e.g., like the satellite-derived winds noted here)

© 2016 H. Michael Mogil

Originally posted 10/4/16

weather

Matthew Plods Along… (H. Michael Mogil, CCM, CBM, DMS)

The overall picture of the future of powerful Hurricane Matthew remains little changed since yesterday. Following a cyclonic loop and a slow course adjustment to the northwest, Matthew is still just moving at a five-mile per hour forward speed. Over the next five days, Matthew is expected to make relatively slow progress as he plods northwestward and then northward. He should be near the latitude of West Palm Beach, FL by early this Friday (Oct. 7, 2016) morning. Earlier computer model runs placed Matthew as far north as the Carolinas by this time.

This provides important information about the forecastability of these storms. While the National Hurricane Center (NHC) has made substantial gains in its ability to forecast where storms like Matthew will go, center errors are still around 175 miles at day 4 (96 hour forecast) and 230 miles at day 5 (120 hours forecast). Errors in intensity are comparably as large or greater.

Early this Sunday morning, Matthew, will his 150-mile per hour sustained winds (Category 4 on the Saffir-Simpson wind scale) was located at 13.9 degrees North latitude and 74.1 degrees West longitude or about 345 miles south-southwest of Port Au Prince, Haiti. Central pressure was 27.76 inches of mercury or about nine percent below average atmospheric pressure. The lower the central pressure in a hurricane, typically, the stronger the hurricane’s wind field.

Hurricane-force winds currently extend outward up to 25 miles, and tropical-storm-force winds extend outward up to 205 miles, from Matthew’s center.

fig001-matthew-120hr-track-161002-8amedtFig. 1 shows current hurricane and tropical storm watches, warnings and advisories associated with Matthew. According to NHC, a warning is typically issued 36 hours before the anticipated first occurrence of tropical-storm- force winds, conditions that make outside preparations difficult or dangerous. A Tropical Storm or Hurricane Watch means that tropical storm or hurricane conditions, respectively, are possible within the watch area.

While Matthew’s winds will likely produce significant structural damage and down trees and power lines, the greater danger may well lie in Matthew’s rainfall potential. Given the slow storm movement, strong winds, and mountainous terrain in his path, total rain accumulations across Haiti should be in the range of 15 to 25 inches, with possible isolated maximum amounts of 40 inches. The risk of flash flooding and mudslides is high. Matthew is also expected to produce total rain accumulations of 10 to 20 inches over eastern Jamaica, the Dominican Republic and eastern Cuba, with possible isolated maximum amounts of 25 inches.

The combination of a dangerous storm surge and large and destructive waves could raise water levels by as much as seven to 11 feet along the south coast of Haiti and somewhat lesser amounts in other coastal areas within the hurricane and tropical storm watch and warnings areas.

Some fluctuations in intensity are possible during the next couple of days due to eye wall replacement cycles, interaction with land, and other factors. But, forecasters expect Matthew to remain a powerful hurricane through Monday night.

Matthew will be close enough to the southeast U.S. coast well into the week. Hence, people along the eastern seaboard from the Carolinas southward should stay abreast of Matthew and his expected track, until the storm has safely passed their latitude. People in other East Coast locations should monitor the storm as Matthew’s impacts may affect these locations by next weekend.

Our correspondent team here at the Global Weather and Climate Center will be posting the latest information and explanations about the storm and about hurricanes, in general.

© 2016 H. Michael Mogil

Originally posted 10/2/16

weather

Powerful Matthew Takes Aim on Jamaica… (H. Michael Mogil, CCM, CBM, DMS)

Overnight, hurricane hunter aircraft and satellite imagery intensity estimates placed Hurricane Matthew in a Category 5 status. A category 5 hurricane is one with sustained winds of 157 miles per hour (137 knots) or more. At 8:00 a.m. E.D.T., on Oct. 1, 2016, Matthew’s winds were estimated to be just below Category 5 strength.

fig001-matthew-120hr-track-161001-8amedtMatthew is now tracking due westward at about 7 miles per hour and is expected to take a turn toward the northwest later today and tonight and then a turn to the north during the next few days (Fig. 1). However, the storm’s slow movement is expected to continue. This makes forward speed a key factor in the storm’s forecast and expected impacts. Viewing the National Hurricane Center (NHC) forecast track and “cone of uncertainty” (the cone that encompasses about two-thirds of the forecast error at different forecast times), Matthew could be spreading storm force winds across Jamaica for almost a full day (with many hours of very strong hurricane force winds). A similar scenario could play out across eastern Cuba. Obviously, beach erosion (associated with strong wind and wave action) will become a significant coastal impact for both islands.

A hurricane watch is in effect for Jamaica and a tropical watch covers parts of southwest Haiti as of early on Oct. 1, 2016.

Heavy rainfall is also a risk, in part due to slow movement and the effect of terrain across these islands. Winds blowing up mountain slopes favor increased rainfall. Narrow valleys allow for channeling of runoff, possible leading to localized flash flooding and mudslides. On the other hand, mountains will act to disrupt the storm structure and weaken the storm. Hence, the forecast calls for Matthew to drop below “major” hurricane status (category 3 or 111 mile per hour winds) by late on Tues., Oct. 4, 2016 (after crossing eastern Cuba).

Storm track is also a consideration because the storm is expected to pass through the Bahamas, close enough to southeast Florida to cause concern. As of early on Oct. 1, the trend toward taking the storm closer to the U.S. mainland persists. However, Canadian and European numerical models have a different solution set, one that places the storm further to the east.

As is always the case, additional data from the latest hurricane hunter aircraft and morning upper level wind observations from U.S. and Caribbean locations will be used in the next round of computer model runs.

It is important to recognize that the average NHC forecast eye position forecast errors are around 175 miles at day 4 (96 hour forecast) and 230 miles at day 5 (120 hours forecast). Hence, NHC notes that it is too soon to rule out possible hurricane impacts in Florida from Matthew.

Here are the official forecast positions from NHC as of 8:00 a.m. E.D.T. on Oct. 1, 2016. Fig. 1 shows these and the error cone.

FORECAST POSITIONS AND MAX WINDS INIT

01/0900Z 13.3N 72.8W  135 KT 155 MPH 12H

01/1800Z 13.3N 73.6W  130 KT 150 MPH 24H

02/0600Z 13.8N 74.5W  120 KT 140 MPH 36H

02/1800Z 14.9N 75.1W  110 KT 125 MPH 48H

03/0600Z 16.2N 75.7W  110 KT 125 MPH 72H

04/0600Z 19.5N 76.0W  110 KT 125 MPH 96H

05/0600Z 23.0N 76.0W   90 KT 105 MPH 120H

© 2016 H. Michael Mogil

Originally posted 10/1/16