MJO Model Forecasts

Saffir-Simpson Hurricane Scale

Category	Wind Speed (mph)	Storm Surge (ft)
5	≥157	>18
4	130–156	13–18
3	111–129	9–12
2	96–110	6–8
1	74–95	4–5
Additional Classifications
Tropical Storm	39–73	0–3
Tropical Depression	0–38	0

The Saffir-Simpson Hurricane Scale is a classification used for most Western Hemisphere tropical cyclones that exceed the intensities of "tropical depressions" and "tropical storms", and thereby become hurricanes. Source: Intellicast

Hurricane Season 101

The official Atlantic Basin Hurricane Season runs from June 1st to November 30th. A tropical cyclone is a warm-core, low pressure system without any “front” attached. It develops over tropical or subtropical waters, and has an organized circulation. Depending upon location, tropical cyclones have different names around the world. The Tropical Cyclones we track in the Atlantic basin are called Tropical Depressions, Tropical Storms and Hurricanes! Atlantic Basin Tropical Cyclones are classified as follows: Tropical Depression: Organized system of clouds and thunderstorms with defined surface circulation and max sustained winds of 38 mph or less. Tropical Storm: Organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds of 39-73 mph. Hurricane: Intense tropical weather system of strong thunderstorms with a well-defined surface circulation. A Hurricane has max sustained winds of 74 mph or higher!

The difference between Tropical Storm and Hurricane Watches, Warnings, Advisories and Outlooks

Warnings: Listen closely to instructions from local officials on TV, radio, cell phones or other computers for instructions from local officials. Evacuate immediately if told to do so.

Storm Surge Warning: There is a danger of life-threatening inundation from rising water moving inland from the shoreline somewhere within the specified area. This is generally within 36 hours. If you are under a storm surge warning, check for evacuation orders from your local officials.
Hurricane Warning: Hurricane conditions (sustained winds of 74 mph or greater) are expected somewhere within the specified area. NHC issues a hurricane warning 36 hours in advance of tropical storm-force winds to give you time to complete your preparations. All preparations should be complete. Evacuate immediately if so ordered.
Tropical Storm Warning: Tropical storm conditions (sustained winds of 39 to 73 mph) are expected within your area within 36 hours.
Extreme Wind Warning: Extreme sustained winds of a major hurricane (115 mph or greater), usually associated with the eyewall, are expected to begin within an hour. Take immediate shelter in the interior portion of a well-built structure.

Please note that hurricane and tropical storm watches and warnings for winds on land as well as storm surge watches and warnings can be issued for storms that the NWS believes will become tropical cyclones but have not yet attained all of the characteristics of a tropical cyclone (i.e., a closed low-level circulation, sustained thunderstorm activity, etc.). In these cases, the forecast conditions on land warrant alerting the public. These storms are referred to as “potential tropical cyclones” by the NWS. Hurricane, tropical storm, and storm surge watches and warnings can also be issued for storms that have lost some or all of their tropical cyclone characteristics, but continue to produce dangerous conditions. These storms are called “post-tropical cyclones” by the NWS.

Watches: Listen closely to instructions from local officials on TV, radio, cell phones or other computers for instructions from local officials. Evacuate if told to do so.

Storm Surge Watch: Storm here is a possibility of life-threatening inundation from rising water moving inland from the shoreline somewhere within the specified area, generally within 48 hours. If you are under a storm surge watch, check for evacuation orders from your local officials.
Hurricane Watch: Huriricane conditions (sustained winds of 74 mph or greater) are possible within your area. Because it may not be safe to prepare for a hurricane once winds reach tropical storm force, The NHC issues hurricane watches 48 hours before it anticipates tropical storm-force winds.
Tropical Storm Watch: Tropical storm conditions (sustained winds of 39 to 73 mph) are possible within the specified area within 48 hours.

Advisories:

Tropical Cyclone Public Advisory:The Tropical Cyclone Public Advisory contains a list of all current coastal watches and warnings associated with an ongoing or potential tropical cyclone, a post-tropical cyclone, or a subtropical cyclone. It also provides the cyclone position, maximum sustained winds, current motion, and a description of the hazards associated with the storm.
Tropical Cyclone Track Forecast Cone:This graphic shows areas under tropical storm and hurricane watches and warnings, the current position of the center of the storm, and its predicted track. Forecast uncertainty is conveyed on the graphic by a “cone” (white and stippled areas) drawn such that the center of the storm will remain within the cone about 60 to 70 percent of the time. Remember, the effects of a tropical cyclone can span hundreds of miles. Areas well outside of the cone often experience hazards such as tornadoes or inland flooding from heavy rain.

Outlooks:

Tropical Weather Outlook:The Tropical Weather Outlook is a discussion of significant areas of disturbed weather and their potential for development during the next 5 days. The Outlook includes a categorical forecast of the probability of tropical cyclone formation during the first 48 hours and during the entire 5-day forecast period. You can also find graphical versions of the 2-day and 5-day Outlook here

Be sure to read up on tons of more information on Hurricane knowledge, preparedness, statistics and history under the menu on the left hand side of the page!

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Madden-Julian Oscillation (MJO)

The Madden–Julian Oscillation (MJO) is the largest element of the intraseasonal (30–90 days) variability in the tropical atmosphere. It is a large-scale coupling between atmospheric circulation and tropical deep convection. Rather than being a standing pattern (like ENSO) it is a traveling pattern, propagating eastwards at approximately 4 to 8 m/s, through the atmosphere above the warm parts of the Indian and Pacific oceans. This overall circulation pattern manifests itself in various ways, most clearly as anomalous rainfall. This was discovered by Roland Madden and Paul Julian (again the comparison with ENSO is instructive, since their local effects on Peruvian fisheries were discovered long before the global structure of the pattern was recognized).

The MJO is characterized by an eastward progression of large regions of both enhanced and suppressed tropical rainfall, observed mainly over the Indian Ocean and Pacific Ocean. The anomalous rainfall is usually first evident over the western Indian Ocean, and remains evident as it propagates over the very warm ocean waters of the western and central tropical Pacific. This pattern of tropical rainfall then generally becomes nondescript as it moves over the cooler ocean waters of the eastern Pacific (except over the region of warmer water off the west coast of Central America) but occasionally reappears at low amplitude over the tropical Atlantic and higher amplitude over the Indian Ocean. The wet phase of enhanced convection and precipitation is followed by a dry phase where thunderstorm activity is suppressed. Each cycle lasts approximately 30–60 days. Because of this pattern, The MJO is also known as the 30–60 day oscillation, 30–60 day wave, or intraseasonal oscillation.