Hurricanes an Overview

What is a Hurricane ?

The Atlantic Hurricane Season begins June 1 and ends November 30 of each year.

Hurricane Isabel 09/18/2003

A hurricane is a Topical Cyclone with sustained winds reaching speeds of 74 mph or higher.

?? Okay.. so whats a Tropical Cyclone..??

Well basically put.. a tropical cyclone has the following characteristics, a warm core low pressure system that develops over tropical (and sometimes subtropical) waters, and has an organized circulation. The categories of these systems are usually based on surface winds and are as follows:

Tropical Disturbance – A discrete tropical weather system of apparently organized convection usually maintaining  itself over period of 24 hours and can be associated with easterly waves off of Africa.

Tropical Depression – When a tropical disturbance develops a closed circulation (e.g., counter-clockwise winds blowing around a center of low pressure), it is categorized as a tropical depression. Tropical depressions contain max. sustained one-minute winds of 38 mph (33 knots) or less, at an elevation of 10 meters.

Tropical Storm – A tropical cyclone is given a name by the National Hurricane Center once it reaches tropical storm status. Tropical storms have maximum sustained one-minute winds of 39-73 mph (34-63 knots).

Current Name List 

Hurricane – Hurricanes have sustained one-minute winds of at least 74 mph (64 knots), at an elevation of 10 meters. Winds in most hurricanes can become much stronger. Hurricanes are categorized on a scale of 1 to 5 based on their wind speed via the Saffir-Simpson Hurricane Wind Scale. (<–See link for types of damage associated each category)

Major Hurricane – A tropical cyclone with maximum sustained winds of 111 mph (96 knots) or higher, corresponding to a Category 3, 4 or 5 on the Saffir-Simpson Hurricane Wind Scale.

Climatology

Number of Tropical Cyclones per 100 Years

The above chart shows the distribution of the number of storms over a 100 hear period. The  peak of the season is from mid-August to late October. However, deadly hurricanes can occur anytime in the hurricane season.

Origination

Below graphic shows also the associated areas where storm originates as the season progresses.

origins

 Whats important to note here is that a hurricane does not necessarily have to originate from Africa.. though those that normally due usually can be more

Tracks

tracks

The figures below show the zones of origin and tracks for different months during the hurricane season. These figures only depict average conditions. Hurricanes can originate in different locations and travel much different paths from the average. Nonetheless, having a sense of the general pattern can give you a better picture of the average hurricane season for your area.

danger     HAZARDS    danger

  • STORM SURGE

    • Along the coast, storm surge is often the greatest threat to life and property from a hurricane. In the past, large death tolls have resulted from the rise of the ocean associated with many of the major hurricanes that have made landfall. Hurricane Katrina (2005) is a prime example of the damage and devastation that can be caused by surge. At least 1500 persons lost their lives during Katrina and many of those deaths occurred directly, or indirectly, as a result of storm surge.

    • Storm surge is an abnormal rise of water generated by a storm, over and above the predicted astronomical tides. Storm surge should not be confused with storm tide, which is defined as the water level rise due to the combination of storm surge and the astronomical tide. This rise in water level can cause extreme flooding in coastal areas particularly when storm surge coincides with normal high tide, resulting in storm tides reaching up to 20 feet or more in some cases.

  • High Winds

    • Tropical storm-force winds are strong enough to be dangerous to those caught in them. For this reason, emergency managers plan on having their evacuations complete and their personnel sheltered before the onset of tropical storm-force winds, not hurricane-force winds.
    • Hurricane force winds of 74 mph or more, can destroy buildings and mobile homes. Debris, such as signs, roofing material, siding and small items left outside become flying missiles during hurricanes. Winds can stay above hurricane strength well inland.

  • Rain / Flooding

    • Tropical cyclones often produce widespread, torrential rains in excess of 6 inches, which may result in deadly and destructive floods. In fact, flooding is the major threat from tropical cyclones for people living inland. Flash flooding, defined as a rapid rise in water levels, can occur quickly due to intense rainfall. Longer term flooding on rivers and streams can persist for several days after the storm. When approaching water on a roadway, always remember Turn Around Don’t Drown.

  • Tornadoes

    • Hurricanes and tropical storms can also produce tornadoes. These tornadoes most often occur in thunderstorms embedded in rain bands well away from the center of the hurricane; however, they can also occur near the eyewall. Usually, tornadoes produced by tropical cyclones are relatively weak and short-lived, but they still pose a significant threat.

We will be posting more on hurricanes as we get closer to the heart of the hurricane season..

Including the Impediments to Storm Development, NHC  Forecasting Models,  NHC Aircraft Reconnaissance, FEMA;s Role and some information on what occurs locally when we are effected by tropical systems.

CURRENT ATLANTIC TROPICAL OUTLOOK

Click on Pic to go to National Hurricane Center for Latest Information

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Hurricane Preparedness Week


Hurricane Season Begins on June 1st 

….are you ready ?  

History teaches that a lack of hurricane awareness and preparation are common threads among all major hurricane disasters. By knowing your vulnerability and what actions you should take, you can reduce the effects of a hurricane disaster.

Hurricane hazards come in many forms, including storm surge, heavy rainfall, inland flooding, high winds, tornadoes, and rip currents. The National Weather Service is responsible for protecting life and property through issuance of timely watches and warnings, but it is essential that your family be ready before a storm approaches. Furthermore, mariners should be aware of special safety precautions when confronted with a hurricane.

Download the Tropical Cyclone Preparedness Guide (PDF) or follow the links for more information. But remember, this is only a guide. The first and most important thing anyone should do when facing a hurricane threat is to use common sense.

Visit——->>>> http://www.nhc.noaa.gov/prepare/

Click on the Above Image to be brought to the NOAA Site

Severe Weather Climatology, Risks and Information

tornado-widescreen-wallpaper-tv00tSevere Weather Climatology

Obviously severe weather can happen all year round, but for the Delaware region most of the threat is usually contained in the late spring and summer months. A severe thunderstorm is one that produces winds 58 mph or stronger and/or hail 1 inch in diameter or larger. Below shows the probability of severe storms in the continental U.S. based on 30 years of climate data. Each frame is one day from March to August.


Majority of the significant threats are wind related and flooding that usually accompanies strong thunderstorms. Tornado activity in the region is not frequent but can occur. A majority of these storms are usually at the low end of the Enhanced Fujita Scale (EF0-EF2). The EF Scale rates the strength of tornadoes in the United States and Canada based on the damage they cause.

EF

The Storm Prediction Center

The Storm Prediction Center (SPC) is part of the National Weather Service (NWS) and the National Centers for Environmental Prediction (NCEP). 2014_SPC-2.1Located in Norman Oklahoma, their mission is to provide timely and accurate forecasts and watches for severe thunderstorms and tornadoes over the contiguous United States. The SPC also monitors hazardous winter weather and fire weather events across the U.S. and issues specific products for those hazards. The SPC uses a suite of products and multiple of specialists from lead forecasters, mesoscale forecasters, outlook forecasters and etc. that continuously monitor the continental US for the potential for severe damaging weather events. (For more info on the SPC go here –> About the SPC)

Risk Categories Associated with SPC’s Outlooks

Here is an example of  a Day One Outlook issued by the SPC and definitions of the categories.

outlooke

Outlook-category-descriptions

The Difference Between Watch and Warning

WHAT IS A WATCH ?

Understanding the purpose of a watch is important and should not be confused with a warning. A warning means that hazardous weather is occurring at the moment / imminent and you should take actions to protect yourself. Below is a full list of categories issued by the SPC and NWS Offices.

Madden-Julian Oscillation (MJO)

What is it ??

There are many weather phenomenon that have repetitive variation to them in which we see different states and respectively different outcomes in the environment and atmosphere. One of these is called the Madden-Julian Oscillation, or simply called MJO.  The MJO was actually founded not until the early 1970’s by  Roland Madden and Paul Julian of the American National Center for Atmospheric Research (NCAR) while observing tropical wind and pressure patterns.

The MJO can be thought of as a tropical disturbance that propagates eastward around the global tropics with a cycle on the order of 30-60 days and it consists of two phases. The first phase is the convective phase or enhanced rainfall and the second is the suppressed rainfall. In the enhanced convective phase, winds at the surface converge, and air is pushed up throughout the atmosphere. At the top of the atmosphere, the winds reverse (i.e., diverge). Such rising air motion in the atmosphere tends to increase condensation and rainfall.

MJO_610

In the suppressed convective phase, winds converge at the top of the atmosphere, forcing air to sink and, later, to diverge at the surface. As air sinks from high altitudes, it warms and dries, which suppresses rainfall. In this circumstance Green is upward unstable environment while the Brown is dry and stable.

Measuring and Forecasting MJO

MJO is forecast in phases ( not to be confused with the  wet phase and dry phase mentioned earlier ) according to which the region of the world its unstable.  Below is a forecast of the MJO as of August 8th 2016.

ensplume_full

This may look little alien as it were but, its actually pretty straight forward.

History is depicted as the Ref line here beginning around June 29th then continuing getting a little more enhanced in Phases 1 & 2 as it continues to more recent observations (blue line ). The forecast is predicted via the green line. The yellow lines in this instance symbol the  individual ensemble members, which all seem to point to strong Phase 5.

Mathematical methods combine cloud amount and winds at upper and lower levels of the atmosphere to provide a measure of the strength and location of the MJO. When the index is within the centre circle the MJO is considered weak and when it is outside of this circle the index is stronger and will usually move in an anti-clockwise direction as the MJO moves from west to east. For convenience, it is defined in 8 different MJO phases / locations in this diagram.  Below is a look at the 8 Phases and how they correlate to locations.

MJOfig1

 

Why do we look at the MJO ?

Remember, this is really a look at the tropics and the conditions of the environment going forward.  When we see MJO in Phases outside 7, 8 and 1 it would tell us the chance of cyclone development is slight because the instability that is needed to keep thunderstorms alive is just not present. Hence why we have not seen much activity in the Main Development Region so far this year.

The MJO also effects weather and climate outside the tropics, in particularly in the mid-latitudes between 40° and 70° in both hemispheres where the prevailing winds are westerly (from the west) and the atmospheric flow pattern is highly variable with alternating low and high pressure systems.  The impacts to North America  may include heavy precipitation or cold outbreaks over time periods of 1-2 weeks. The MJO impacts the western U.S. through “teleconnections,” a term that refers to climate anomalies having a relationship between each other at large distances (typically thousands of kilometers). For example, rainfall in the Indian Ocean associated with the MJO is often related to cooler and wetter weather in the western U.S.

Summary

So the MJO plays just another part of the wonderful world of fluid dynamics that affect our weather. They tend to have usually pretty consistent effects for us here in the east but can be mitigated by other factors as well. As we head into the heart of the hurricane this just one of many items to monitor as indication of more favorable cyclone genesis.

July Hurricanes and Review of the Outlook

Typical July Climatology Surrounding Hurricanes

We have all heard that this years Hurricane Season is suppose to be Normal to Above Normal in terms of events, yet it is July and it is so quiet.. why? Well we thought we’d take a minute or two to explain the current conditions and why this is usually the norm.

First off is the Atlantic Basin, in July we usually see a typical set up of a strong High Pressure and sequentially strong Trade Winds in the Main Development Region (MDR).

gfs_pres_wind_atl_3

The relevant effect of this is usually extremely dry air and dust pushed off the Africa continent.

We have talked a bit about this dust prior in our Hurricanes: What is SAL post, but to recap :

Saharan Air Layer (SAL) – SAL is a dry air mass driven off of Saharan Desert and can sometimes be abundant with dust. This elevated layer of Saharan air and mineral dust occurs during the late spring through early fall over extensive portions of the North Atlantic Ocean between the Sahara Desert, the West Indies, and the United States. Dry air will definitely suppress thunderstorms and weaken tropical cyclones causing downdrafts to occur around the storm and in turn inhibit hurricane development.

Below is an image of SAL taken on July 15th, 2016 the yellow and red show the great amount of dry air / SAL currently in the MDR.

sal

Typically in late summer we should see a shift and weakening of the High Pressure and subsequently a reduction in SAL, however; this is a significant detriment to the development of tropical cyclones and is watched through the entire season.

One of the other factors that usually are a good inhibitor is the presence of Wind Shear in the Gulf and the Caribbean Looking at current conditions though we have some areas of 20+ knots of wind shear its not overwhelming right now .

wg8sht-1

The one other item worth mentioning is the current positioning of the tropical waves and precipitable water, this is also typical in the early hurricane season. This is noticeable in the SAL image above but you can also see it here in the below satellite pic. 

waves

The MDR usually is between 10°N (Red Line) and 20°N. These storms are traveling across the Atlantic and right now feeding the activity in the pacific. This will change as we head into August as the Monsoonal Trough moves northward.

We basically have covered most of the items surrounding why July is usually a slow month for hurricanes but, we do have them historically. In fact we usually don’t look to the East Atlantic for these storms to develop, they usually occur closer to home. Here is a map outlying where storm development occurs by month:

tracks

Hurricane Outlooks for 2016

We discussed why July is so slow typically but what about the months going forward. First statement we would like to make is that it’s anybody’s guess. Yes we said  ‘guess’ , there are so many competing factors when it comes to storm development, intensity, path, and timing that prediction of hurricanes is a very difficult and volatile especially when we are talking seasonal forecasting. Yet there are some fundamental meteorological and atmospheric conditions that can guide us in understanding what may occur during the 2016 Hurricane Season and we will try to cover them here.

ENSO and the Atlantic Multi-Decadal Oscillation (AMO)

El Nino / La Nina  along with sea surface temperatures usually have a dominant influence on the Hurricane season.

Here is what we typically expect for relative to ENSO influences on the Hurricane Season :

ENSOTypicalElNino_610 (1)

ENSOTypicalLaNina_610 (1)

As notated in the graphics El Nino / La Nina impacts are primarily caused by changes in the vertical wind shear, which refers to the change in wind speed and direction between roughly 5,000-35,000 ft. above the ground. Strong vertical wind shear can rip a developing hurricane apart, or even prevent it from forming.

Now we can take a look at July’s SST Anomalies (departure from normal) where you can see a huge difference year on year.

**********  2015 El Nino Year  **********

anomw.7.16.2015(1)

**************  2016 CURRENT  ***************

anomw.7.14.2016 (1)

As you can see what a change year on year.. we are seeing a more La Nina type pattern emerging as we head into the Hurricane Season but we are currently in a Neutral ENSO for mid July.  Here is the outlook prepared in June with respect to an emerging La Nina: (clicking below chart will bring you to the CPC ENSO Page)

probalnina

The CPC / IRI forecast currently a 71% chance of La Nina

during the prime hurricane months of Aug. Sept. and Oct.

Atlantic Multi-Decadal Oscillation (AMO)

The  AMO is an ongoing series of long-duration changes in the sea surface temperature of the North Atlantic Ocean, with cool and warm phases that may last for 20-40 years at a time. Since late 1990’s we have been in a warm phase. During warm phases of the AMO, the numbers of tropical storms that mature into severe hurricanes is much greater than during cool phases, at least twice as many per NOAA. The switch form Warm phase to Cold phase is hard to predict and NOAA has noted its uncertainty relative to the AMO for the 2016 Hurricane Season.

Current SST from OSPO NOAA

Looking at current SSTs does look as the Atlantic is primed for the Hurricane Season. Hurricanes usually like temps of 79°F (26°C) or greater that definitely doesn’t look like an issue here.

In synopsis  a “La Nina does favor a stronger Hurricane Season by producing more conducive atmospheric conditions within the MDR, including 1) weaker vertical wind shear resulting primarily from weaker upper-level westerly winds, 2) decreased sinking motion, and 3) decreased stability. However, the overall hurricane season strength depends not only on La Niña, but also on the phase of the AMO. If La Niña develops, an above-normal season would be much more likely if the warm AMO signal also appears. A near-normal season would be most likely if La Niña develops but the warm AMO signal does not appear.”

NOAA 2016 Hurricane Outlook

NOAA 2016 Hurricane Outlook

So what we mentioned earlier about good ‘guess..’ it still applies here.. why.. because all this information just really just tells us about the chances of hurricane developing and how active the season will be. IT IS NOT A LAND FALLING FORECAST ! Realistically you live in the Mid Atlantic region ( our assumption ) and well historically we don’t have lot of land falling hurricanes but it doesn’t mean we shouldn’t be prepared. We do, and have had impacts from tropical systems. July is the slow month and should be used as preparation of a ‘What If..” scenario. Most of our region will shelter place but if you live along the Coast and or Delaware River know your evacuation routes have a plan developed that you an your family can execute and rely on in case of impacts. Visit www.ready.gov to create a plan.

Winter Patterns

Is Winter Finally On The Way ??

Well it has been a while since we’ve posted here on the blog.. mostly because the weather has been mostly typical of a Strong El Nino where our temps have been well above normal up to this point with no ‘severe’ winter weather events in our area. Now though, we are beginning to transition into the winter as El Nino begins to weaken and the pattern begins to change for the remainder of the season..

We will begin to look at changing patterns of the atmosphere that can last days, weeks, and even months. This is  what we call teleconnection patterns. Teleconnection refers to a recurring and persistent, large-scale pattern of pressure and circulation anomalies that spans vast geographical areas in the atmosphere.

Okay Great… So What this All Mean ??

So lets try to go through and give you a graphical representation of each to explain how a -NAO -AO and +PNA are the best set up for a Mid-Atlantic / East Coast for winter storm setup.

Below is a look at characteristics of a Negative / Positive Arctic Oscillation (AO)

ao

You can see here in a negative phase that the cold in the stratosphere is basically displaced into Canada and North America.

Here is a graphical representation of a North Atlantic Oscillation (NAO) and its general effects:

NAO2A Negative NAO  is also sometimes referred as the Greenland Block , East Based NAO because high pressure establishes itself there allowing for the strongest flow of cold into the Mid Atlantic. West based NAO where high is positioned move over Canada is little less favorable.

… and Finally A Look at the Pacific North American (PNA) Pattern

ElNino_Mod (1)

Image by Steve Tracton (2010)

Positive PNA is also sometimes referred to as  a ‘zonal flow’ usually brings milder conditions from the west straight along to the east.

So wait then, why did we see snow then here in December of 2013 where the patterns didint match any of these and we still got good snow fall totals ???

There is another pattern called the East Pacific Oscillation (EPO)

 The EPO is the high altitude  wind flow over the Eastern Pacific which is influenced by the ocean temps.. When the EPO is in a positive phase, there is usually troughing on the West Coast, while milder air engulfs the inland and Eastern part of the country. The positive EPO limits troughs in the East.  When the EPO is in a negative phase it has the opposite effect on the East Coast where a -EPO encourages a northwesterly flow from Canada into the Eastern part of the U.S, allowing for cold air to intrude, but without the assistance of a stronger -AO or -NAO we end up with more transient shots of cold air  that usually support snow more west of the coastal plain as we saw in 2013.

Water Temperatures – This early into the year, water temps usually dont help us on the coastal plain that much. It is usually not till we get more into the heart of the winter season when water temps get cooler and have a less dramatic effect on potential snow storms.

Finally Storm Track – Inland storms also favor snow to west and rain to the east.. with a south to south west wind bring warm temps during the storm,  and then cold air as the system moves out with slight chance of snow on the back-end.

Okay so what are we seeing today that may be indication that winter is coming ?

We have already mentioned that the El Nino is beginning to weaken. Though El Ninos typically mean more wintry type pattern for the mid-atlantic, strong ones can actually have the reverse effect. In term of the teleconnections we will take a look at where we are as of today (12.29.15).

AO – Trending Negative
get_orig_img (2)

NAO – Trending Neutral to Negative

get_orig_img (3)

PNA – Positive

get_orig_img (4)

EPO – Slightly Negative

get_orig_img (5)

So in summary as it looks as we are beginning a transition to more colder pattern it could also spell a more wintry one as well. Yet we dont want to get ahead of ourselves and be as bold to say a snowy harsh winter is on the way.  Just because we are trending colder does not mean we will be getting a snow storm soon. Water temps right now make coastal plains not a good bet for snow especially if there’s a prevailing east wind.

Looking forward is always hard to do in the world of weather nothing is ever final or definite, but there are signs here we are taking notice of as we head in 2016 !

HAPPY NEW YEAR !

ny20162

Flood Safety Awareness Week

taddbarrierApril 6th – 10th 2015taddbarrier

newark

Flooding is a coast to coast threat to the United States and its territories nearly every day of the year. NOAA has designed a page  to teach you how to stay safe in a flood event. If you know what to do before, during, and after a flood you can increase your chances of survival. There you will find an interactive flood map, information describing the different types of flooding, educational material, and resources on how the National Weather Service keeps you aware of potentially dangerous flooding situations.

VISIT:: http://www.floodsafety.noaa.gov/index.shtml

Hearns Pond Dam - IMG_2187Delaware Flood Information

http://www.floodsafety.noaa.gov/states/de-flood.shtml

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Ash Wednesday Storm 1962