Southern hemisphere tropical weather

Tropical weather in the southern hemisphere does not really follow a season similar to that seen in the North Atlantic and Eastern Pacific. Instead, tropical storms have developed throughout the year and the tropical season can be said to last from July all the way to June. Of course their seasons are opposite of the seasons in the northern hemisphere so the heaviest activity occurs from November through April.


The chart above shows the total number of tropical cyclones from 1969 - 2006 in both the southern Indian and the South Pacific Oceans by month. The average number of storms in a given year is 28.25 and every year had over 20 named storms.

Reference: Southern Hemisphere Monthly Storm Distribution (Australian Severe Weather)

While the southern hemisphere is clearly more active than any of the northern basins, the potential for landfall is much less since the land area in the south is less than in the north.

Anja was the first storm of the year forming on November 15th, the start of the peak period for the south. This storm is expected to not make landfall prior to breaking apart later in the week.

We have not covered southern storms in the past. As information is available, we will attempt to provide links and content for readers in the southern latitudes. The sources I utilize may not have detailed information for southern cyclones and much of that information may be in French (see previous post).

Additionally, those of us in the north need to keep in mind that the rotation of the Earth causes tropical cyclones to rotate clockwise in the southern hemisphere as can be seen in this picture of Anja.

Likewise the directional tendencies will be to the south and east rather than to the north and west as we see in the Atlantic and Eastern Pacific.

Photo source: Anja premier cyclone tropical (Grandbaie.mu)

Another difference between the northern and the southern hemisphere is the tropical cyclone classification system shown above. These classifications differ from the Saffir-Simpson scale used in the Atlantic and Eastern Pacific basins. Categories are based on the averaged 10 minute sustained winds in knots converted to km/hr.

Source: Tropical Cyclone Map Intensity Scale Information (Australian Severe Weather)

The definitions in the following table are from the Southern Hemisphere classification system (as used by the Australian BoM), and all maps on this website have been plotted using it. JTWC best track data has been converted from 1-minute average winds in knots, to the Southern Hemisphere standard of 10-minute average winds in knots, then converted to km/h. The conversion used is "JTWC 1-min" * 0.88 * 1.852. Operational data is also converted using this formula where 10-min average winds are not available.

The Hurricane and Typhoon classification systems are different.

Tropical Cyclone Anja to affect Rodrigues

Tropical Cyclone Anja continues to grow in the south Indian Ocean now reaching the equivalent of a Cat 3 storm and ecpected to grow to Category 4 on the Saffir-Simpson scale. Initially it appeared that this storm would not affect any landmasses. Now, projections indicate that it will come close to the island of Rodrigues in the south Indian Ocean.

The island will be affected by the outer bands of the storm but the heaviest winds and rain will remain out to sea. Rodrigues is the northeastern most of the Mascarene islands which make up the nation of Mauritius. The other islands should not be affected by the cyclone.

Cyclone Anja: Océan Indien Sud (Mateo World)

Le premier cyclone de la saison s’est formé dans l’Océan Indien.

Baptisé hier après midi sous le nom de Anja, le cyclone s’est renforcé en un cyclone de catégorie 2/5 ce matin, avec des vents qui soufflent à 148 km/h en moyenne, et des rafales allant jusqu’à 208 km/h près du centre.

Anja fait actuellement du surplace, mais devrait se diriger vers le sud de l’océan Indien, épargnant ainsi toutes les îles situées dans le sud de l’océan Indien.

English translation courtesy of Google Translate

Anja had been essentially stationary over much of the weekend as she traversed an arc from a northwesterly direction to the southeast. Now Anja's forward speed has been increasing with a current forward speed of 12 km/hr.

Le cyclone Anja à 1.585 kilomètres à l'Est-Nord-Est (Zinfos 974)

A 10 heures locales ce matin, Anja présentait une pression équivalente à 950 hectopascals en son centre et était centré par les points suivants : 14.1 Sud et 68.9 Est, ce qui le positionne à 1.585 kilomètres à l'Est-Nord-Est de nos côtes.

Pour le moment, le cyclone tropical poursuit sa route en direction du Sud-Ouest à la vitesse de 12 km/h et se rapproche lentement et sûrement de Rodrigues dont il était distant de 925 kilomètres selon le dernier bulletin émis par les services météorologiques mauriciens.

Le CMRS (Centre météorologique régional spécialisé) précise, par ailleurs, que les rafales maximales mesurées étaient de 221 km/h à 10 heures tandis que les vents moyens mesurés sur 10 minutes étaient équivalents à 157 km/h.

English translation courtesy of Google Translate

Anja is expected to weaken back to tropical storm stregnth over the next 48 hours along with a sharp turn to the southeast.

Tropical Cyclone Anja grows in the S. Indian Ocean

Tropical Cyclone 1S became TC Anja today is it grew from a tropical storm to a cyclone with category 2 level winds.

Topical systems in the Indian Ocean basin are known as Tropical Cyclones regardless of the storm's intensity.

Yesterday's forecast indicated that Anja would remain as a tropical storm until early int he week and then grow to a Cat 1 storm before diminishing. Now indications are that Anja will grow to a Cat 3 level storm by Sunday night local time and remain as a severe cyclone until mid week whe conditions result in a sudden drop in intensity as well as faster forward motion including a turn from the southwest to the south-southeast.

Public Advisory (Weather Underground)

Is IDA coming back?

Is Ida going to become the "Storm That Never Ends?

AccuWeather is speculating that the remnants of Hurricane Ida may circulate back around in the Atlantic throughtout this coming week and drive up the east coast again next week.

Will Ida Return Next Week? (AccuWeather)

Ida will depart the East Coast later this weekend, but will that be the last time the United States deals with the storm? There are a few indications that the answer may be no.

Saturday into Tuesday, Ida's remains will slowly creep southeastward through the Atlantic Ocean. Beyond that point, it cannot be totally ruled out that Ida gets steered back westward and poses another threat to the East Coast.

Graphic courtesy of AccuWeather.

A forecast this far in advance is admittedly uncertain. So how could the low pressure center that was Ida come back to strike the east coast again? The graphic below shows the overall upper level air circulation pattern. The graphic itself is from Spaghettimodels.com. Your humble hurricane hobbiest added the indicators designating the three high pressure systems and the possible pathway that Ida could take.

Ida's low will be moving to the east today out into the ocean. High pressure coming east from Ohio and another high in the northern Gulf of Mexico will help to drive the low away from the coast this weekend. The canadian high that has helped fuel the Nor'easter along with Ida will prevent the low from drifting northward.

There is also a clockwise circulation in the Atlantic (I assume this is a high pressure system as well but I did not see that indicated on any maps). The low of Ida could become caught in the circulation and pulled towards the south. Then as the week continues, the same circulation could drive this low back around into the Bahamas and then north towards the Carolinas.

We will have to watch this system to see what happens as the week progresses. Looking at the sea surface temperatures, the water near Florida and the Bahamas is warm enough for tropical development but the wind shear is increasing from the Bahamas all the way north to the mid-Atlantic states. Wind shear will make development unlikely.

Remnants of Ida causing trouble in New England

Remnants from Hurricane Ida continue to pound the northeast coast today creating extreme weather from New Jersey all the way up to southern Maine. Winds of 25 - 45 MPH will continue along with wave heights of 8 - 16 feet. The conveyor system set up by Ida's low pressure and the Canadian high has shifted northward pushing the storms winds and rain directly from the east onto the coast.

New England Dreary from Ida`s Rain (AccuWeather)

Moisture from Ida will advance into New England today, bringing a soggy start to the weekend from New Jersey to southern Maine. It will be a cloudy and at times dreary November day elsewhere in the Northeast.

Unlike the storm's dire outcome in the Southeast, widespread flooding rain and damaging winds will not plague New England this weekend. However, rough surf and gusty winds will continue to pummel the coastal areas of the mid-Atlantic and New England.

Ida`s Winds Deliver Final Blow (AccuWeather)

Gusty onshore winds will continue today in the mid-Atlantic and New England. While winds will be much weaker today compared to recent days in the mid-Atlantic, there could still be some isolated damage.

Generally the strongest gusts of 20-30 mph will be directed at areas from Ocean City, Md., to Boston. Isolated gusts of up to 45 mph could also howl in this corridor. In communities where the highest gusts blow, some tree branches could be downed. There could also be sporadic power outages.

The storm is expected to move out to sea and ending the rain and winds today.
Graphics courtesy of AccuWeather

Remnants of Hurricane Ida pounding US east coast

After making landfall in the northern Gulf of Mexico as a tropical storm, Ida headed due east and lost her tropical characteristics. As a low pressure system in the Atlantic, however, the storm has retains enough counter-clockwise circulation to fuel a strong Nor'easter causing flooding and heavy rain from North Carolina up to New Jersey.

This storm system has begun to cause deaths due to the wigh waves and strong surf.

Huge Waves and Coastal Flooding Risk (AccuWeather)

Large waves will continue to surge into the mid-Atlantic coast today into Saturday before subsiding, reducing the coastal flooding threat. Strong winds are being fueled between Tropical Rainstorm Ida off the North Carolina coast and an area of high pressure dominating the Canadian Maritimes. Winds are pushing ocean water toward the coast, leading to battering waves.

This is a very dangerous situation for anyone planning to venture near or into the water over the next few days. Very rough surf and deadly rip currents are expected from North Carolina to southeastern New England.

One of the five deaths being blamed on Tropical Rainstorm Ida includes a 36-year-old man surfing at a New York City beach Thursday. He died after getting caught in dangerous surf.

A high pressure system located near the Canadian maritimes is creating a conveyor-belt effect with Ida's remains that is accelerating winds and generating a large storm surge.

The system is expected to move towards New England and then out to sea. The effects of the storm should decrease as it heads further north.

Ida Pounding the Mid-Atlantic to Southeast New England(AccuWeather)

A slow-moving nor'easter that was once Hurricane Ida will continue lashing the mid-Atlantic today into Saturday with high winds. Winds will also increase farther up the coast from Long Island to southeastern New England.

The damage is not expected to be as severe the farther north you go because wind gusts will not be quite as strong. From coastal areas of Virginia to southeastern New England, wind gusts will reach 60 mph.

The strong onshore flow will also continue to push ocean water to the coast today, threatening coastal flooding and beach erosion for areas from the hard-hit beaches of North Carolina all the way to southeastern Massachusetts.

Although Ida has not been classified as a hurricane or even a tropical storm since it made landfall in Alabama, wind speeds in this Nor'easter have reached hurricane strength in some areas. Winds of 65 - 75 MPH were recorded overnight in Virginia along with rainfall of as much as 13 inches.

The big Nor'Easter begins to wind down (Weather Channel)

Between low pressure just east of the Outer Banks and strong high pressure over New England and the Canadian Maritimes, wind, rain, coastal flooding and battering waves continue to plague the East Coast from Nantucket and Long Island to the Jersey shore, the Delmarva Peninsula, Tidewater Virginia and northeast North Carolina.

Areas around the Virginia/North Carolina border have picked up from 8 to 13 inches of rain. Through tonight, 1-to-3-inch rains will focus on coastal New Jersey, much less than has been experienced farther south.

Last evening, the winds peaked with this storm as Chesapeake Bay Bridge Tunnel, Cape Henry, Norfolk and Oceana gusted to between 70 and 75 mph, causing many power outages. Into tonight, winds will gust to between 40 and 50 mph from Nantucket and Long Island to the Jersey shore and the Delmarva Peninsula. The risk for power outages will expand northward with these winds.

Strong winds will focus on southeast Massachusetts on Saturday, possibly gusting to over 50 mph on Nantucket.

The persistent onshore flow will also result in more coastal flooding, beach erosion and high waves. The water rises combined with the high tides have approached historic levels of 5 to nearly 8 feet in SE Virginia, not seen since the big nor'easters in January and February of 1998 and Isabel in 2003.

Graphics courtesy of AccuWeather