0

Insight: Assessing The Looming Threat From Hurricane Matthew

By DR JEFF MASTERS

Director of Meteorology

Weather Underground

Matthew is weaker as it meanders over the central Caribbean south of Haiti, but the mighty Category 4 hurricane is expected to move northwards later on Sunday and deliver a punishing blow to the islands of Hispaniola, Cuba and Jamaica on Monday and Tuesday.

An Air Force hurricane hunter aircraft made three passes through the eye of Matthew on Sunday morning, and found that Matthew’s winds had weakened to 140mph and the central pressure had risen to 947 mb.

This weakening may be partially due to the fact Matthew has essentially stalled, allowing the storm to bring up cooler waters from below. In addition, satellite loops on Sunday morning showed that Matthew had wrapped some dry air into its circulation, and this may have contributed to weakening of the storm.

Moderate wind shear of 10 to 20 knots is affecting Matthew, and the storm is over warm ocean waters of 28.5°C (83°F) and has plenty of moisture to work with: 75 to 80 per cent relative humidity at mid-levels of the atmosphere, as analysed by the Statistical Hurricane Intensity Prediction Scheme (SHIPS) model. The outer spiral bands of Matthew can be seen on Jamaican radar.

Matthew will pass within 50 miles of National Oceanic and Atmospheric Administration (NOAA) buoy 42058 late this afternoon. At 9.50am EDT Sunday, winds at the buoy were 47 mph, gusting to 56 mph, and seas were 23 feet.

Two-day track forecast

Despite Matthew drifting a bit further westward than expected on Sunday morning, the models are very unified in their two-day track forecasts for Matthew.

A large upper-level low pressure system over east-central United States will pull Matthew to the north through Tuesday, resulting in a landfall or a near-miss in southwest Haiti on Monday night, followed by a second landfall in eastern Cuba/northwest Haiti on Tuesday morning.

Matthew will then continue northwards into the southeastern Bahamas on Tuesday afternoon.

In their 11am EDT Sunday Wind Probability Forecast, the National Hurricane Centre (NHC) gave highest odds of hurricane-force winds to Les Cayes in southwest Haiti (35 per cent) and to Guantanamo Bay, Cuba (31 per cent). Lower odds were given to Kingston, Jamaica (6 per cent), and Port-Au-Prince, Haiti (6 per cent).

Two-day intensity forecast

The latest SHIPS model forecast predicts that wind shear will steadily drop during the next two days, becoming very low, less than 5 knots, by Monday afternoon. At the same time, ocean temperatures will warm to 29°C (84°F) and the heat content of the ocean will increase, which ordinarily would argue for re-intensification of Matthew.

However, this morning’s observation that dry air was getting wrapped into the circulation may mean that intensification will struggle to occur today and Monday. Furthermore, this morning’s hurricane hunter flight showed evidence of a secondary maximum in winds outside of the eyewall. This may be an indication that Matthew could undergo an eyewall replacement cycle (ERC), where the inner eyewall collapses and is replaced by a larger-diameter eye, with a new eyewall formed from an outer spiral band.

This process usually causes a weakening to the storm’s top winds for a day or so. The down side of an ERC is that is spreads out the storm’s hurricane-force winds over a wider area, resulting in severe impacts over a wider area.

Our top three intensity models - the HWRF, LGEM, and SHIPS models - were predicting on Sunday morning that Matthew would be at Category 3 or 4 strength at landfall on Monday evening. The SHIPS model gave Matthew a 0 per cent probability of rapid intensification of 30mph or more by Monday morning. All factors considered, a Category 3 hurricane at landfall Monday night is probably the most likely scenario.

It is unknown what role, it any, the unusual blob of heavy thunderstorms that has persisted on Matthew’s east side might play in the future evolution of the storm. If this intense area of thunderstorms remains intact through Monday night, it could result in catastrophic rains for Haiti.

Longer-range intensity forecast

Matthew’s anticipated landfall over Jamaica/Cuba/Haiti on Monday will weaken the storm, due to the high mountains it will interact with.

However, it now appears that Matthew will have limited time over land, due to the storm’s expected track mostly over the water areas between Haiti and Cuba. While this is good news for those nations, this would be bad news for the Bahamas.

Matthew’s inner core may be able to survive the land interaction, resulting in a much stronger storm in the Bahamas. The latest 12Z Sunday SHIPS model forecast predicts low to moderate wind shear, a very moist atmosphere and near-record warm ocean temperatures near 30°C (84°F) for Matthew later this week when it is over the Bahamas, so we can expect strengthening.

Matthew is likely to be a major Category 3 or stronger hurricane for at least a portion of its trek through the Bahamas. As Matthew moves north of the Bahamas, waters will cool and the shear is likely to increase, resulting in some weakening late this week.

Longer-range track forecast

Over the past two days, our two best computer models have been trending towards a more westerly track for Matthew late this week, increasing the odds that Matthew will make a direct hit somewhere along the US East Coast. Sunday’s 00Z European model and 06Z GFS model had Matthew coming very close to or making landfall in North Carolina 6 to 7 days from now. As one can see from the latest set of ensemble model runs, just about any location along the East Coast could potentially see a hurricane landfall this week. Since the hurricane is expected to be moving roughly parallel to the coast, a long stretch of the coast may receive strong winds and heavy rain from Matthew.

We do have three decent models predicting a path for Matthew well away for the US coast late in the week, though - the HWRF, Canadian and GFDL - so it is not yet a foregone conclusion that Matthew will impact the US coast.

98L: A potential steering influence on Matthew?

An area of low pressure associated with a tropical wave that (designated Invest 98L by the NHC on Sunday morning) is over the central tropical Atlantic several hundred miles east-northeast of the northern Lesser Antilles, and may alter the steering currents for Matthew.

Over 50 per cent of the members of the 00Z Sunday European ensemble forecasts predicted that this system would develop into a tropical depression or tropical storm as it heads northwest at about 15mph early this week; the GFS model showed virtually no development.

In their 8am EDT Sunday Tropical Weather Outlook, the NHC gave this system two-day and five-day odds of development of 20 per cent and 30 per cent, respectively. If this storm develops significantly, it may exert a steering influence on Matthew that could help pull it out to sea.

Satellite loops on Sunday morning showed that 98L had a very limited amount of heavy thunderstorm activity that was poorly organised, thanks to dry air and high wind shear of 25 to 30 knots. The 12Z Sunday SHIPS model forecast predicted wind shear would rise even higher by Tuesday - in excess of 50 knots - so I doubt 98L will be able to develop.

Dr Jeff Masters co-founded Weather Underground in 1995 and flew with the National Oceanic and Atmospheric Adminstration ‘Hurricane Hunters’ from 1986 to 1990. This is his blog from www.wunderground.com yesterday.

Comments

Use the comment form below to begin a discussion about this content.

Sign in to comment