Category 6™

Massive African Dust Storm Cooling Atlantic Hurricane Odds for Early August

By: JeffMasters, 3:10 PM GMT on July 31, 2013

A massive dust storm that formed over the Sahara Desert early this week has now pushed out over the tropical Atlantic, and will sharply reduce the odds of tropical storm formation during the first week of August. The dust is accompanied by a large amount of dry air, which is making the Saharan Air Layer (SAL) much drier than usual this week. June and July are the peak months for dust storms in the Southwest Sahara, and this week's dust storm is a typical one for this time of year. Due in large part to all the dry and dusty air predicted to dominate the tropical Atlantic over the next seven days, none of the reliable computer models is predicting Atlantic tropical cyclone formation during the first week of August.


Figure 1. A massive dust storm moves off the coast of Africa in this MODIS image taken at 1:40 UTC July 30, 2013. Image credit: NASA.


Video 1. The predicted movement through August 3 of this week's Africam dust storm, using the NOAA NGAC aerosol model. Image credit: NOAA Visualization Laboratory.

How dust affects hurricanes
Saharan dust can affect hurricane activity in several ways:

1) Dust acts as a shield which keeps sunlight from reaching the surface. Thus, large amounts of dust can keep the sea surface temperatures up to 1°C cooler than average in the hurricane Main Development Region (MDR) from the coast of Africa to the Caribbean, providing hurricanes with less energy to form and grow. Ocean temperatures in the MDR are currently 0.7°F above average, and this anomaly should cool this week as the dust blocks sunlight.

2) The Saharan Air Layer (SAL) is a layer of dry, dusty Saharan air that rides up over the low-level moist air over the tropical Atlantic. At the boundary between the SAL and low-level moist air where the trade winds blow is the trade wind inversion--a region of the atmosphere where the temperature increases with height. Since atmospheric temperature normally decreases with height, this "inversion" acts to but the brakes on any thunderstorms that try to punch through it. This happens because the air in a thunderstorm's updraft suddenly encounters a region where the updraft air is cooler and less buoyant than the surrounding air, and thus will not be able to keep moving upward. The dust in the SAL absorbs solar radiation, which heats the air in the trade wind inversion. This makes the inversion stronger, which inhibits the thunderstorms that power a hurricane.

3) Dust may also act to produce more clouds, but this effect needs much more study. If the dust particles are of the right size to serve as "condensation nuclei"--centers around which raindrops can form and grow--the dust can act to make more clouds. Thus, dust could potentially aid in the formation and intensification of hurricanes. However, if the dust acts to make more low-level clouds over the tropical Atlantic, this will reduce the amount of sunlight reaching the ocean, cooling the sea surface temperatures and discouraging hurricane formation (Kaufman et al., 2005.)


Figure 2. Map of the mean summer dust optical thickness derived from satellite measurements between 1979 and 2000. Maximum dust amounts originate in the northern Sahel (15° to 18° N) and the Sahara (18° to 22° N). The Bodele depression in Chad is also an active dust source. Image credit: Evidence of the control of summer atmospheric transport of African dust over the Atlantic by Sahel sources from TOMS satellites (1979-2000), by C. Moulin and I. Chiapello, published in January 2004 in Geophysical Research Letters.

Dust in Africa's Sahel region and Atlantic hurricane activity
The summertime dust that affects Atlantic tropical storms originates over the southwestern Sahara (18° - 22° N) and the northwestern Sahel (15° - 18° N) (Figure 3.) The dust from the Southwest Sahara stays relatively constant from year to year, but the dust from the Northwest Sahel varies significantly, so understanding this variation may be a key factor in improving our forecasts of seasonal hurricane activity in the Atlantic. The amount of dust that gets transported over the Atlantic depends on a mix of three main factors: the large scale and local scale weather patterns (windy weather transports more dust), how wet the current rainy season is (wet weather will wash out dust before it gets transported over the Atlantic), and how dry and drought-damaged the soil is. The level of drought experienced in the northwestern Sahel during the previous year is the key factor of the three in determining how much dust gets transported over the Atlantic during hurricane season, according to a January 2004 study published in Geophysical Research Letters published by C. Moulin and I. Chiapello. In 2012 (Figure 3), precipitation across the northwestern Sahel was much above average, which should result in less dust than usual over the Atlantic this fall, increasing the odds of a busy 2013 hurricane season.


Figure 3. Rainfall over the Northwest Sahel region of Africa was about 200% of average during the 2012 rainy season. The heavy rains promoted vigorous vegetation growth in 2013, resulting in less bare ground capable of generating dust. Image credit: NOAA/Climate Prediction Center.

The future of African dust: highly uncertain
A September 2013 paper in the Bulletin of the American Meteorological Society by Joseph Prospero and Olga Mayol-Bracero, "Understanding the Transport and Impact of African Dust on the Caribbean Basin," discusses the large uncertainties on how African dust may change due to climate change. Over the past decade, there has been no clear relationship between African dust and climate indices such as rainfall in the Sahel or the El Niño/La Niña cycle, which "makes it difficult to predict how dust emissions and transport might change over the coming decades as climate changes. The problem is exacerbated by the inability of models (IPCC 2007) to agree on future rainfall trends over large areas of North Africa (including the Sahel) that are known to be major dust sources today and in the recent past."

Links
Saharan Air Layer Analysis from the University of Wisconsin

Atlantic dust forecast from the Tel-Aviv University Weather Research Center

The Saharan Air Layer (SAL) was first described in 1972, in this classic paper: Carlson, T. N., and J. M. Prospero (1972), The Large-Scale Movement of Saharan Air Outbreaks over the Northern Equatorial Atlantic, Journal of Applied Meteorology, 11(2), 283-297

Dr. Amato Evan published a study in Science magazine March 2009 showing that 69% of the increase in Atlantic sea surface temperatures over the past 26 years could be attributed to decreases in the amount of dust in the atmosphere.

Kaufman, Y. J., I. Koren, L. A. Remer, D. Rosenfeld, and Y. Rudich, 2005a: The effect of smoke, dust, and pollution aerosol on shallow cloud development over the Atlantic Ocean. Proc. Natl. Acad. Sci. USA, 102, 11 207–11 212.

Wang, Chunzai, Shenfu Dong, Amato T. Evan, Gregory R. Foltz, Sang-Ki Lee, 2012, Multidecadal Covariability of North Atlantic Sea Surface Temperature, African Dust, Sahel Rainfall, and Atlantic Hurricanes, J. Climate, 25, 5404–5415.
doi: http://dx.doi.org/10.1175/JCLI-D-11-00413.1

Jeff Masters

Hurricane

Flossie Causes Little Trouble for Hawaii; Dorian's Remnants Falling Apart

By: JeffMasters, 3:25 PM GMT on July 30, 2013

A weakening Tropical Depression Flossie passed through the Hawaiian islands on Monday evening and Tuesday morning with little fanfare, bringing scattered wind gusts of tropical storm force and a few areas of heavy rains of 1 - 2". The storm brought down a few trees and power lines, knocking out power for about 6,500 people on Maui and the Big Island. Kahului on Maui recorded sustained winds of 33 mph, gusting to 46 mph, at 7 pm local time Monday. Flossie brought 0.79" of rain to the airport, which was a record for the date. Powerful waves pounded the northwest shore of the Big Island, with significant wave heights of 14' recorded at the Hilo buoy Monday afternoon. Satellite images show that Flossie has lost all of its heavy thunderstorms, and has dissipated. Hawaii has a new storm to watch, though: Tropical Depression Seven-E, which has formed off the coast of Mexico, and is taking a track that may bring it withing 500 miles of Hawaii next week.


Figure 1. MODIS satellite image of Tropical Depression Flossie taken at approximately 20:50 UTC Monday July 29, 2013. At the time, Flossie had top winds near 35 mph. Image credit: NASA.

Remains of Dorian falling apart
The remains of Tropical Storm Dorian, located a few hundred miles north of the Dominican Republic, are headed west to west-northwest at 10 - 15 mph. Satellite images show that ex-Dorian has almost no heavy thunderstorms, and is being torn up by wind shear. In their 8 am EDT Tropical Weather Outlook, NHC gave Dorian's remains a 20% chance of regenerating by Thursday. The primary impediment to development is the presence of an upper-level trough of low pressure to its west that ex-Dorian is running into. Strong upper-level southwesterly winds associated with this trough are creating a moderate 15 - 20 knots of wind shear and driving dry air into the west side of ex-Dorian. This shear is not expected to relent at all during the next few days. None of the reliable computer models for tropical cyclone genesis predict that ex-Dorian will regenerate. Dorian's remains should continue moving west-northwest during the week, spreading over the Bahamas Wednesday and Thursday and over Florida on Friday.

Jeff Masters

Hurricane

Weakening Flossie Closes in on Hawaii; ex-Dorian More Organized

By: JeffMasters, 3:40 PM GMT on July 29, 2013

A weakening Tropical Storm Flossie is closing in on Hawaii, where tropical storm warnings are flying for the entire island chain. Satellite images show that Flossie has lost most of its heavy thunderstorms, and continued weakening is expected as the storm traverses the islands, due to moderate wind shear and dry air aloft. Flossie's winds of 45 mph will likely drop to the 35 - 40 mph range as it passes through the islands on Monday afternoon and evening, and it is possible that no location in Hawaii will record sustained winds of tropical storm force (39 mph or greater.) Monday's 11 am EDT wind probability forecast from the Central Pacific Hurricane Center gave Honolulu a 16% chance of tropical storm force winds, 20% for Kahului on Maui, and no odds for the Big Island. The storm's main threat will be heavy rains. Rainfall amounts of 6 - 10" are expected over The Big Island and Maui, and 4 - 8" in Oahu. Rains of this magnitude are capable of causing dangerous flash flooding and mudslides. Radar loops show a respectable area of heavy rain associated with Flossie, approaching the Big Island.


Figure 1. MODIS satellite image of Tropical Storm Flossie taken at approximately 5 pm EDT Sunday July 28, 2013. At the time, Flossie had top winds near 65 mph. Image credit: NASA.

Tropical storms are uncommon in Hawaii
On average, between four and five tropical cyclones are observed in the Central Pacific every year. This number has ranged from zero, most recently as 1979, to as many as eleven in 1992 and 1994. August is the peak month, followed by July, then September. Tropical storms and hurricanes are uncommon in the Hawaiian Islands. Only eight named storms have impacted Hawaii in the 34 year period 1979–2012, an average of one storm every four years. Since 1949, the Hawaiian Islands received a direct hit from just two hurricanes--Dot in 1959, and Iniki in 1992. Both hit the island of Kauai. Only one tropical storm has hit the islands since 1949--an unnamed 1958 storm that hit the Big Island. A brief summary of the three most significant hurricanes to affect Hawaii in modern times:

September 1992: Hurricane Iniki was the strongest, deadliest, and most damaging hurricane to affect Hawaii since records began. It hit the island of Kauai as a Category 4 on September 11, killing six and causing $2 billion in damage.

November 1982: Hurricane Iwa was one of Hawaii's most damaging hurricanes. Although it was only a Category 1 storm, it passed just miles west of Kauai, moving at a speed of nearly 50 miles per hour (80 km/h). Iwa killed one person and did $250 million in damage, making it the second most damaging hurricane to ever hit Hawaii. All the islands reported some surf damage along their southwest facing shores, and wind damage was widespread on Kauai.

August 1959: Hurricane Dot entered the Central Pacific as a Category 4 hurricane just south of Hawaii, but weakened to a Category 1 storm before making landfall on Kauai. Dot brought sustained winds of 81 mph with gusts to 103 mph to Kilauea Light. Damage was in excess of $6 million. No Dot-related deaths were recorded.


Figure 2. Tracks of all tropical storms and hurricanes to pass within 100 miles of the Hawaiian Islands, 1949 - 2012. During that time span, the Hawaiian Islands received a direct hit from just two hurricanes--Dot in 1959, and Iniki in 1992. Both hit the island of Kauai. One tropical storm also hit, and unnamed 1958 storm that hit the Big Island of Hawaii. Image credit: NOAA/CSC.

Remains of Dorian growing more organized
The remains of Tropical Storm Dorian, located just north of Puerto Rico, are headed west to west-northwest at 15 - 20 mph. Satellite images show that ex-Dorian has a moderate area of heavy thunderstorms that have grown more organized this morning, with an intense clump of thunderstorms that have created a circular area of high cirrus clouds called a Central Dense Overcast (CDO) over the disturbance. There are no signs of a surface circulation on visible satellite images, but an AIr Force hurricane hunter aircraft is on call to investigate ex-Dorian Monday afternoon, if necessary. In their 8 am EDT Tropical Weather Outlook, NHC gave Dorian's remains a 40% chance of regenerating by Wednesday. I put these odds higher, at 50%. The primary impediment to development is the presence of an upper-level trough of low pressure to its west that ex-Dorian is running into. Strong upper-level southwesterly winds associated with this trough are creating a moderate 15 - 20 knots of wind shear and driving dry air into the west side of ex-Dorian. This shear is not expected to relent at all during the next few days. None of the reliable computer models for tropical cyclone genesis predict that ex-Dorian will regenerate, though the HWRF model, which is not reliable for predicting genesis, does show Dorian regenerating. Dorian's remains should continue moving west-northwest during the week, spreading over the Bahamas on Tuesday and Wednesday, and over Florida and Central Cuba on Thursday and Friday.

Philadelphia sets its all-time single day rainfall record
An incredible deluge of 8.02" of rain hit Philadelphia, Pennsylvania on Sunday, breaking the all-time one-day rainfall record for the city. The previous record of 6.63" was set on September 16, 1999 during Tropical Storm Floyd. With a further round of rain after midnight in Philadelphia (bringing the 24-hour record storm total to 8.27”), July has brought 13.25” of precipitation to the City of Brotherly Love. This surpasses the previous July monthly record (since 1872) of 10.42”set in 1994. The wettest month on record for Philadelphia remains 19.31” in August 2011. Yesterday's deluge is an astonishing rainfall total for a location with such a long period of record, considering that it occurred without the benefit of a tropical storm being present. Remarkably, 6.46" of the rain fell in just 3 1/2 hours.

Jeff Masters

Hurricane

Tropical Storm Flossie Takes Aim at Hawaii

By: JeffMasters, 3:15 PM GMT on July 28, 2013

In the Central Pacific, Tropical Storm Flossie, a strong tropical storm with 65 mph winds, is headed west at 20 mph towards Hawaii. Satellite images show that Flossie is maintaining a modest area of heavy thunderstorms that are well-organized. The storm is over waters of 25°C, which is about 1°C below the water temperature typically needed to sustain a tropical storm. Flossie peaked in intensity Saturday morning, when the storm had 70 mph winds. As Flossie approaches the Big Island of Hawaii on Monday, these waters will warm to 26°C, but wind shear is expected to be in the moderate range, which should keep Flossie from strengthening. Dry air aloft will likely cause some weakening before landfall Monday morning, and Flossie will likely have top winds of 45 - 55 mph when is passes through the Hawaiian Islands. Flossie's main threat will be heavy rains, with 6 - 10" expected over The Big Island and Maui County, and 4 - 8" in Oahu. Rains of this magnitude are capable of causing dangerous flash flooding and mudslides. Sunday's 11 am EDT wind probability forecast from the Central Pacific Hurricane Center gave Hilo on the Big Island a 33% chance of experiencing sustained tropical storm force winds of 39 mph or greater from Flossie. These odds were 32% for Honolulu and 41% for Kahului.


Figure 1. MODIS satellite image of Tropical Storm Flossie taken at approximately 5 pm EDT Saturday July 27, 2013. At the time, Flossie had top winds near 50 mph. Image credit: NASA.

Tropical storms are uncommon in Hawaii
On average, between four and five tropical cyclones are observed in the Central Pacific every year. This number has ranged from zero, most recently as 1979, to as many as eleven in 1992 and 1994. August is the peak month, followed by July, then September. Tropical storms and hurricanes are uncommon in the Hawaiian Islands. Only eight named storms have impacted Hawaii in the 34 year period 1979–2012, an average of one storm every four years. Since 1949, the Hawaiian Islands received a direct hit from just two hurricanes--Dot in 1959, and Iniki in 1992. Both hit the island of Kauai. Only one tropical storm has hit the islands since 1949--an unnamed 1958 storm that hit the Big Island. A brief summary of the three most significant hurricanes to affect Hawaii in modern times:

September 1992: Hurricane Iniki was the strongest, deadliest, and most damaging hurricane to affect Hawaii since records began. It hit the island of Kauai as a Category 4 on September 11, killing six and causing $2 billion in damage.

November 1982: Hurricane Iwa was one of Hawaii's most damaging hurricanes. Although it was only a Category 1 storm, it passed just miles west of Kauai, moving at a speed of nearly 50 miles per hour (80 km/h). Iwa killed one person and did $250 million in damage, making it the second most damaging hurricane to ever hit Hawaii. All the islands reported some surf damage along their southwest facing shores, and wind damage was widespread on Kauai.

August 1959: Hurricane Dot entered the Central Pacific as a Category 4 hurricane just south of Hawaii, but weakened to a Category 1 storm before making landfall on Kauai. Dot brought sustained winds of 81 mph with gusts to 103 mph to Kilauea Light. Damage was in excess of $6 million. No Dot-related deaths were recorded.


Figure 2. Tracks of all tropical storms and hurricanes to pass within 100 miles of the Hawaiian Islands, 1949 - 2012. During that time span, the Hawaiian Islands received a direct hit from just two hurricanes--Dot in 1959, and Iniki in 1992. Both hit the island of Kauai. One tropical storm also hit, and unnamed 1958 storm that hit the Big Island of Hawaii. Image credit: NOAA/CSC.

Remains of Dorian are worth watching
The remains of Tropical Storm Dorian will be passing just north of northern Lesser Antilles Islands today and just north of Puerto Rico tonight. Satellite images show no signs of a surface circulation, and just a moderate area of heavy thunderstorms associated with the storm. AIr Force hurricane hunter aircraft are on call to investigate Dorian's remains on Sunday afternoon and Monday afternoon, if necessary. In their 8 am EDT Tropical Weather Outlook, NHC gave Dorian's remains a 20% chance of regenerating by Tuesday.

Extreme heat wave in Europe
An extreme heat wave is baking Europe today, and at least five countries have a chance at setting a new all-time national heat record. The most likely candidate is Liechtenstein, where the forecast for Balzers Sunday calls for a high of 95°F. According to wunderground's International Records database maintained by our weather historian, Christopher C. Burt, the current all-time heat record for Liechtenstein is 36°C (96.8°F) set at Vaduz on August 13, 2003.

Jeff Masters

Hurricane

The Beta Effect

By: Lee Grenci , 2:51 PM GMT on July 27, 2013

Yesterday I talked about the steering of tropical cyclones by the mean wind in a steering layer determined by the system's minimum central pressure (revisit the relevant graphic). For strong hurricanes, the steering layer spans a large portion of the troposphere. For example, the steering layer for a hurricane with minimum central pressure between 940 mb and 949 mb spans from 850 mb (roughly 5000 feet) to 250 mb (roughly 35000 feet). The mean wind in this layer (the "steering wind") accounts for roughly 80% to 90% of the hurricane's motion.

As I briefly mentioned yesterday, about 10% to 20% of the storm's motion arises from the Beta effect. You might think that forecasting the track of tropical cyclones would thus be "child's play." But modeling the Beta effect isn't easy. The Beta effect gets even more complicated when tropical cyclones are moving briskly and undergoing rapid changes in intensity. Lesson learned: Predicting the tracks of tropical cyclones, though forecasters continue to improve, is not an exact science. Sometimes, it's far from it.


Hurricanes moving due westward tend to drift northwestward in time. Why? Stay tuned.

What is the Beta effect? For starters, let's agree to restrict our discussion to the Atlantic Ocean in the Northern Hemisphere. In a nutshell, the Beta effect arises from the variation of the Coriolis parameter with latitude. This variation of the Coriolis parameter is the primary reason why hurricanes forming at low latitudes tend to drift northwestward (see schematic above) from their westward track (for simplicity, I'm assuming here that the mean wind in the deep steering layer blows from east to west across the Atlantic Ocean).

Before we delve into the nuts and bolts of the Beta effect, I need to make sure that all my readers are on the same page with regard to some of the basic concepts about vorticity that are relevant to this discussion. First, vorticity is simply the measure of the spin around an axis. For the most part, synoptic meteorologists are interested in the spin around the local vertical, which is simply a line drawn from a point on the earth's surface to the center of the earth (here's an idealized schematic of a few local verticals, courtesy of A World of Weather: Fundamentals of Meteorology). This "vertical vorticity" (spin around a local vertical) is not fast by most standards. For sake of comparison, the vertical vorticity of a tornado with a diameter of 100 meters is roughly 10,000 to 100,000 times greater than the vertical vorticity that's relevant in synoptic meteorology. Nonetheless, such seemingly slow spin plays a pivotal role in weather.


An idealized schematic showing a 500-mb ridge (left) and a 500-mb trough (right). 500-mb height lines are the thin, dark contours, and the capsule-shaped features represent air parcels. Note how an air parcel moving through the ridge gains anticyclonic spin (negative relative vorticity) and an air parcel moving through the trough gains cyclonic spin (positive relative vorticity). Courtesy of A World of Weather: Fundamentals of Meteorology.

There are two sources of vorticity that weather forecasters weigh. The first is relative vorticity, which is generated by the curvature of isobars or height contours on a constant pressure surface. For example, an air parcel shaped like a Tylenol capsule acquires relative vorticity as it simply flows through 500-mb troughs and ridges (check out this idealized schematic above, courtesy of A World of Weather: Fundamentals of Meteorology). To get your bearings, the contours that form the ridge and trough are 500-mb height lines. At any rate, air parcels acquire cyclonic vorticity (by convention, a positive number) as they round the bend in the trough, and anticyclonic vorticity (negative relative vorticity) as they negotiate the curve in the ridge.


Horizontal wind shear produces anticyclonic relative vorticity in a 500-mb ridge (left) and cyclonic relative vorticity near the base of a 500-mb trough (right). Courtesy of A World of Weather: Fundamentals of Meteorology.

Horizontal wind shear, which is the change in wind speed and/or wind direction over a horizontal distance, is also a source of relative vorticity. In the idealized schematic above, air parcels appear as little fans. The green vectors represent the wind (the longer green vectors correspond to faster winds). And so, you can get the sense that horizontal wind shear in troughs and ridges cause the fans to rotate, creating cyclonic vorticity in the trough and anticyclonic vorticity in the ridge.

The second type of vertical velocity is planetary vorticity (alternatively, earth vorticity), which is spin around a local vertical induced by the rotation of the earth (check out the idealized schematic below, courtesy of A World of Weather: Fundamentals of Meteorology). Note that earth vorticity increases with increasing latitude. In other words, earth vorticity at the equator is zero, and earth vorticity at the North Pole is a maximum. The relatively small values of earth vorticity in the Tropics accounts for the reason why tropical cyclones must form a minimum distance of 500 kilometers (about 300 miles) from the equator (in order to develop a cyclonic circulation). There are exceptions to this rule, of course...Typhoon Vamei in 2001, for example.


Earth vorticity increases from zero at the equator to a maximum at the North Pole. Courtesy of A World of Weather: Fundamentals of Meteorology.

Back to the basics of vertical vorticity (I'll sometimes drop the "vertical" and simply write, "vorticity." At any rate, absolute vorticity is simply the sum of relative vorticity and earth vorticity. Okay, we're ready to delve into the Beta effect and to understand why hurricanes moving due west tend to drift northwestward with time (to see what I mean, check out the first slide of the flash animation below). As you read through the following paragraph, please revisit this flash animation, which you can advance by clicking on the forward button in the upper-right corner.


The Beta effect helps to control the movement of tropical cyclones (the mean wind in the steering layer controls 80% to 90% of the storm's movement). Explore the nifty flash animation above to see why (click on the forward button in the upper-right corner). In general, the Beta effect causes westward-moving storms to move to the right (N.H.) of the steering wind (the mean wind in the steering layer). In the absence of a steering wind, an apparently motionless hurricane will drift toward the northwest in response to the Beta effect (I'm assuming we're in the Northern Hemisphere). Courtesy of Penn State's online Certificate Program.

Okay, air parcels moving southward on the western flank of the tropical cyclone's center lose earth vorticity. On the eastern side of the storm, northward-moving air parcels gain earth vorticity (the Coriolis parameter, which depends on latitude, increases with increasing latitude). As it turns out, absolute vorticity associated with hurricanes tends to be conserved above the boundary layer. Thus, the relative vorticity of southward-bound air parcels must increase on the hurricane's western flank to offset their loss of earth vorticity. Similarly, the relative vorticity of northward-bound parcels must decrease on the eastern flank of the storm to compensate for their gain in earth vorticity. As a result, two centers of positive and negative relative vorticity form to the west and east of the hurricane's center (respectively). In response, two secondary circulations develop (cyclonic around the center of positive relative vorticity, and anticyclonic around the center of negative relative vorticity). Please note that you can't observe these circulations on satellite loops because their orders of magnitude are so much smaller than the hurricane's circulation.

Nonetheless, these circulations associated with the Beta effect are sufficiently large to cause a westward-moving hurricane to drift northwestward. Moreover, the Beta effect is the reason why tropical cyclones flirting with crossing the equator swerve to the northeast before it's too late.

To my knowledge, there haven't been any tropical cyclones that have crossed the equator, but a few have come close, particularly in the northern Indian Ocean. But is it possible, Grenci? I would answer "yes." That's because a tropical cyclone's relatively large cyclonic relative vorticity would not initially be affected by the weak change in the Coriolis force as it crossed into the opposite hemisphere (eventually, of course, the circulation of a hemisphere-swapping hurricane would become anticyclonic and dissipate). And, as I just discussed, the Beta effect works against any crossover.


A clockwise-rotating disturbance over the North Atlantic on June 26-27, 2008. Apparently, the disturbance crossed the equator from the Southern Hemisphere. Courtesy of CIMSS.

Still, I can't deny that there are equator-crossing disturbances. To see what I mean, check out case of a anticyclonically rotating disturbance that apparently originated in the Southern Hemisphere and then crossed the equator into the Northern Hemisphere on June 27, 2008 (see satellite animation above). In my opinion, some really cool stuff!

Here endeth the lesson.

Lee

Hurricane

The Steering of Dorian

By: Lee Grenci , 3:54 PM GMT on July 26, 2013

The 5 A.M. discussion from the National Hurricane Center indicated that Tropical Storm Dorian "lost organization" as it encountered southwesterly wind shear and middle- to upper-tropospheric dry air (one of the traditions I learned from the late John Hope was to never use "he" or "she" to describe a named tropical cyclone). NHC's discussion also focused on low- to middle-tropospheric winds associated with the the Atlantic subtropical high-pressure system (06Z GFS model analysis of 700-mb heights early this morning) as the primary steering currents for Tropical Storm Dorian (see the 06Z GFS model analysis of 700-mb heights and 700-mb streamlines below (larger image). At the time, Dorian was moving to the west-northwest at 17 knots.



The 06Z GFS model analysis of 700-mb heights and 700-mb streamlines on July 26, 2013. 700-mb wind speeds are color-coded in knots. Larger image. Courtesy of Penn State.

When I was a young forecaster (a long, long time ago), I typically looked at mid-tropospheric winds as a proxy for the general movement of tropical cyclones. That's because mid-tropospheric winds serve as a rough approximation for the mean airflow in the troposphere. More specifically, old timers like me looked at the winds between 700 mb and 500 mb at a radius of approximately five to seven degrees latitude from the center of the storm (one degree latitude equals 60 nautical miles). As it turns out, winds in the layer from 700 mb to 500 mb often tend to correlate best with the movement of tropical cyclones (at these radii, environmental winds are essentially unaltered by the circulation associated with the tropical cyclone).

Obviously, my approach as a young forecaster was old school. Nonetheless, my simple method had some merit. Indeed, research has shown that a deep-layer mean flow (between 1000 mb to 100 mb, for example) can be used as a tool to assess steering currents (this technique captures the spirit of my old-school approach).

Subtropical highs are not the only features that steer tropical cyclones. Indeed, mid-latitude systems (500-mb troughs, for example) can also steer tropical cyclones as they move poleward from the Tropics. At times, two tropical cyclones can steer each other, assuming that they're close enough for their circulations to interact (the Fujiwhara effect...a topic for a future blog). Finally, tropical cyclones contribute to their own steering, especially when steering currents are rather weak (the Beta effect, which is fodder for another future blog).


The variation of the steering layers for tropical cyclones with minimum central pressure. Larger image. Courtesy of CIMSS and Dr. Chris Velden.

That's all well and good, Grenci, but why did NHC specifically reference "low- to mid-tropospheric winds in their 5 A.M. discussion today? Experience gained from the careful observations of operational forecasters eventually prompted further research aimed at establishing the connection between the minimum pressure of a tropical cyclone and the corresponding depth of the steering layer. The bar graph above (larger image), which displays the minimum pressure of tropical cyclones versus the depth of their steering layers in the Atlantic basin, supports the notion that the steering layer for a tropical depression is shallower and resides lower in the troposphere. In contrast, the steering layer for strong hurricanes is much deeper. The simple physical connection for you to take away after reading my blog is that a weak tropical cyclone (like Dorian) is usually associated with a shallow vortex. Thus, the mean wind in a correspondingly shallow and low-level layer serves as the steering current. As a general rule, the deeper the vortex, the deeper the layer mean that steers the tropical cyclone.


The 09Z analysis of the streamlines designating the mean wind in the layer from 850 mb to 700 mb on July 26, 2013. Larger image. Courtesy of CIMSS.

To get a better sense for the movement of Dorian, focus your attention on the first layer on the left of the bar graph above (central pressure between 1000 mb and 1010 mb). The steering current for Dorian and other similarly weak tropical storms boils down to the mean wind between 850 mb (roughly 5000 feet) and 700 mb (10000 feet). The 09Z analysis from CIMSS (above; larger image) indicates the streamlines of the mean wind in the layer between 850 mb and 700 mb. Wind speeds are color-coded in knots.

At the other end of the spectrum, note the deep steering layers for strong tropical cyclones whose central pressures are lower than 940 mb or range from 940 mb to 949 mb.

I should point out that these results do not include the impact of the Beta effect on the movement of a tropical cyclone. Moreover, other factors such as season, latitude, easterly versus westerly environmental flow, the rates at which the intensity of tropical cyclones changes with time, etc., probably can skew these results a bit, but, as a general rule, the bar graph above will get you in the ballpark in all the ocean basins.

We've come a long way since I was a young forecaster.

Lee

Hurricane Tropical Meteorology

Little Change to Dorian as it Heads West-Northwest

By: JeffMasters, 3:31 PM GMT on July 25, 2013

Tropical Storm Dorian continues steaming west-northwest at 17 mph across the middle of the Atlantic Ocean with little change in appearance this morning. Satellite images show that Dorian is a small but well-organized system with a moderate amount of heavy thunderstorms. Although Dorian is a small storm, it has tapped into a large area of moisture to its southwest associated with the Intertropical Convergence Zone (ITCZ), and has significantly moisturized its environment. A large area of dry air still lies to Dorian's west, as seen on water vapor satellite images. Dorian is under a low 5 - 10 knots of wind shear, which will tend to allow slow development. Ocean temperatures are barely adequate for maintaining strength of a tropical storm, about 25.5°C, but are now on the rise.


Figure 1. This morning's 00Z GFS model was run 20 different times at low resolution with slight perturbations to the initial fields of temperature, moisture, pressure, and winds. This ensemble of forecasts for Dorian is presented here in the pink lines, with the regular high-resolution forecast in white. The ensemble shows that the long-range track of Dorian is likely to follow one of two paths: a sharp recurvature to the north, missing the U.S., or a continued west-northwest path into the Bahamas, Florida, or Cuba.

Forecast for Dorian
The band of moist, unstable air to its southwest that has been feeding Dorian the past two days is forecast to get cut off on Friday, which will leave the storm isolated in a region with relatively dry, stable air. However, the SHIPS model predicts that wind shear will stay in the low range through Sunday, so there may be no mechanism to drive dry air into the storm to weaken it significantly. Ocean temperatures will begin to rise significantly next two days, reaching 27°C by Friday night and 28°C by Sunday. This increase in water temperature may counteract the more stable air Dorian will be in, allowing the storm to maintain its strength. Given its small size, Dorian is capable of relatively large changes in intensity in a short amount of time, and it would not surprise me if the storm dissipated by the end of the week--or became a Category 1 hurricane. The official NHC forecast of a tropical storm passing just north of the Lesser Antilles on Sunday is the most likely outcome; the 11 am wind probability forecast from NHC gave Dorian a 25 - 32% chance of being a hurricane at that time. Since Dorian is a small storm, the impacts to the northern Lesser Antilles Islands may be minor, if the core of the storm passes more than 50 miles to the north of the islands, as the official NHC forecast currently anticipates. It currently appears that Dorian will be a potential threat to the Bahama Islands, Bermuda, and the U.S. East Coast next week. There will be a trough of low pressure capable of recurving Dorian out to sea before the storm reaches the Bahamas and U.S., but it is uncertain if this trough will be strong enough to do the trick.

The Friday and Saturday updates on Dorian will be later than usual this week, as I am traveling on the West Coast.

Jeff Masters

Hurricane

Tropical Storm Dorian Forms

By: JeffMasters, 3:48 PM GMT on July 24, 2013

The season's fourth named storm, Tropical Storm Dorian, is here. Born from a strong tropical wave that moved off the coast of Africa on Monday, Dorian formed unusually far east for so early in the season, at longitude 29.9°W. Only Hurricane Bertha of 2008, which became a tropical storm at 22.9°W longitude on July 3, formed farther to the east so early in the year. Satellite images show that Dorian is a small but well-organized system with a moderate amount of heavy thunderstorms. A large area of dry air lies to Dorian's west, as seen on water vapor satellite images, but Dorian has moistened its environment enough that this dry air should not interfere with development for the next day. Dorian is under a low 5 - 10 knots of wind shear, which will tend to allow slow development. Ocean temperatures are barely adequate for maintaining strength of a tropical storm, about 26.5°C.


Figure 1. MODIS satellite image of Tropical Storm Dorian taken at approximately 8 am EDT July 24, 2013. At the time, Dorian had top winds near 50 mph. Image credit: NASA.

Forecast for Dorian
The SHIPS model predicts that wind shear will stay in the low range through Thursday, then rise to the moderate range Friday through Monday. Ocean temperatures will fall to 25 - 26°C Wednesday night through Thursday night, which may induce some weakening of Dorian. Thereafter, ocean temperatures will rise again, but wind shear will rise. This increase in wind shear will be capable of causing weakening, since there will still be a large area of dry air to Dorian's west that the shear may be able to bring into Dorian's core. Given its small size, Dorian is capable of relatively large changes in intensity in a short amount of time, and it would not surprise me if the storm dissipated by the end of the week--or became a Category 1 hurricane. However, the official NHC forecast of a tropical storm passing just north of the Lesser Antilles on Sunday is the most likely outcome; the 11 am wind probability forecast from NHC gave Dorian a 6% chance of being a hurricane at that time. Dorian should maintain a west-northwest track through the week, and spread heavy rains and gusty winds to the northern Lesser Antilles Islands beginning on Sunday. The usually reliable European model (ECMWF) has Dorian passing several hundred miles to the north of the Lesser Antilles Islands, while the other models show Dorian passing closer, within 100 miles. It currently appears that Dorian will be a potential threat to the Bahama Islands, Bermuda, and the U.S. East Coast next week. There will be a trough of low pressure capable of recurving Dorian out to sea before the storm reaches the Bahamas and U.S., but this trough is currently depicted as being fairly weak, reducing the chances of Dorian missing the Bahamas and U.S. East Coast.


Figure 2. Tracks of all Atlantic tropical depressions, tropical storms, and hurricanes (tropical cyclones) occurring in the months of June and July off the coast of Africa. Only Bertha of 2008 became a named storm farther east so early in the year, compared to Tropical Storm Dorian. Reliable satellite records of Eastern Atlantic tropical cyclones go back to 1966. Image credit: NOAA/CSC.

Jeff Masters

Hurricane

African Tropical Wave 98L Moving Over Cooler Waters

By: JeffMasters, 2:23 PM GMT on July 23, 2013

A strong and well-organized tropical wave that moved off the coast of Africa on Monday (98L) is located a few hundred miles south of the Cape Verde Islands and is moving west-northwest at 15 - 20 mph. Satellite images show that 98L has a decent amount of spin, but only a modest amount of heavy thunderstorms that have not changed much in intensity or areal coverage this morning. The wave is under a moderate 10 - 20 knots of wind shear, which will tend to allow slow development. A large amount of dry air lies to the north and west of 98L, and this dry air will likely interfere with development later this week. The SHIPS model predicts that wind shear will stay in the moderate range through Saturday. Ocean temperatures are barely adequate for development, about 26.5°C today, and will be below average over the region of ocean 98L will be traversing on Wednesday and Thursday, 25 - 26°C. These temperatures are very marginal for development. The Madden Julian Oscillation (MJO), a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days, does not favor increased chances of Atlantic tropical cyclone formation this week. The reliable computer models for tropical cyclone genesis do not predict that 98L will develop this week. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave 98L a 40% chance of developing into a tropical cyclone by Thursday. 98L should maintain a west-northwest track through the week, and may spread heavy rains and gusty winds to the northern Lesser Antilles Islands beginning on Saturday night or on Sunday.


Figure 1. Satellite image of 98L off the coast of Africa taken at 8 am EDT Tuesday July 23, 2013, with a satellite analysis of where dry air is, as well. A large amount of dry air lies to the north and west of 98L, and will likely interfere with development later this week. Image credit: University of Wisconsin CIMSS and NOAA/HRD.

Jeff Masters

Hurricane

African Tropical Wave 98L a Marginal Threat to Develop

By: JeffMasters, 3:38 PM GMT on July 22, 2013

A strong and well-organized tropical wave moved off the coast of Africa on Monday, and has been designated 98L by NHC. This disturbance is headed west at 10 - 15 mph, and is under a moderate 10 - 15 knots of wind shear. A large amount of dry air lies to the north and west of 98L, and will likely interfere with development. The SHIPS model predicts that wind shear will stay in the moderate range through Thursday, then rise to the high range, 20 - 30 knots, on Friday and Saturday. Ocean temperature are warm off the coast of Africa (27 - 28°C,), but will cool to 25 - 26°C on Tuesday through Thursday, a temperature that is quite marginal for development. None of the computer models predict that 98L will develop, not even the usually aggressive Canadian (CMC) model. In their 8 am EDT Monday Tropical Weather Outlook, NHC gave 98L a 10% chance of developing into a tropical cyclone by Wednesday. 98L should maintain a west to west-northwest track through the week, and may bring heavy rains and gusty winds to the northern Lesser Antilles Islands beginning on Saturday night.


Figure 1. Satellite image of 98L off the coast of Africa taken at 8 am EDT Monday July 22, 2013, with a satellite analysis of where dry air is, as well. A large amount of dry air lies to the north and west of 98L, and will likely interfere with development. Image credit: University of Wisconsin CIMSS and NOAA/HRD.


Figure 2. MODIS satellite image of 98L taken at approximately 8 am EDT July 22, 2013. Image credit: NASA.

Jeff Masters

Hurricane

NHC's Tropical Weather Outlook: How Accurate are its Predictions?

By: JeffMasters, 2:46 PM GMT on July 20, 2013

Every Internet-savvy tropical weather enthusiast is familiar with the National Hurricane Center's Tropical Weather Outlook (TWO), which details potential threat areas that might become a tropical cyclone. (Tropical depressions, tropical storms, and hurricanes are all tropical cyclones.) The Tropical Weather Outlook is issued four times per day during hurricane season, and beginning in 2010, NHC began issuing 48-hour forecasts of the probability that specific threat areas identified in the TWO could develop into a tropical cyclone. Their Graphical Tropical Weather Outlook now color-codes each threat area depending upon how likely development is expected to be. A yellow circle is drawn for 0%, 10%, and 20% chances; orange for 30%, 40% and 50% chances, and red for 60% and higher odds. For example, the Saturday morning, July 20 TWO gave a 0% chance of development for an area of disturbed weather near the Florida Panhandle (Figure 1.)


Figure 1. NHC's Tropical Weather Outlook for 8am EDT July 20, 2013, showed an area of disturbed weather over the Gulf of Mexico being given a 0% chance of development in 48 hours. In 2012, 8% of all disturbances being given a 0% chance of development actually did develop.

How accurate is NHC's Tropical Weather Outlook?
So the big question is, how good are these forecasts? When NHC gives a 30% chance that an "Invest" will become of tropical cyclone, does this happen 30% of the time? Well, according to the 2012 National Hurricane Center Forecast Verification Report, NHC should have drawn fewer yellow circles and more orange circles and red circles during 2012, as there was a tendency to under-predict when a threat area might develop. For example (Figure 2), for the 46 forecasts where a 30% chance of development was given, 50% of the threat areas actually developed. Every disturbance that was given a 70% and higher chance of development ended up developing. This under-prediction tendency in 2012 is in contrast to the results from 2011, when the genesis forecasts were closer to the mark. For example, the 59 forecasts for a 30% chance of development resulted in a 31% "hit" rate of the storm actually developing in 2011. So far in 2013, there seems to be a tendency to under-predict again. For example, 48 hours before Tropical Storm Barry developed, NHC was carrying just a 10% chance of development.




Figure 2. NHC did predictions on new formation of a tropical depression or tropical storm (cyclogenesis) beginning in 2010. The forecasts are expressed in the Tropical Weather Outlook in 10% probability increments, and in terms of categories (“low”, “medium”, or “high”) for a tropical cyclone forming within a 48-hour period. These genesis forecasts had a low (under-forecast) bias in the Atlantic basin during 2012 (top). For example, for cases where a 30% chance of formation was given, the actual percentage of storms that formed was 50%. However, there the 2011 forecasts showed no systematic bias, and were closer to the mark (bottom.)

Expansion of the Tropical Weather Outlook to 5 Days
By August of the 2013 hurricane season, NHC is planning to begin including information about a system’s potential for development during the following five-day period. This will supplement the 48-hour probabilistic formation potential already provided in the Tropical Weather Outlook. NHC is currently developing a corresponding five-day genesis potential graphic that might also be available in 2013.

Quiet in the Atlantic
There are no other tropical cyclone threat areas in the Atlantic to discuss today. Saturday morning's 06Z run of the GFS model predicted that a tropical wave expected to move off the coast of Africa on Monday will develop later in the week. None of the other reliable models develop this wave, though the unreliable Canadian (CMC) model also suggests that the wave could develop.

Have a great weekend, everyone, and I'll be back Monday with a new post.

Jeff Masters

Hurricane

Earth has its 5th Warmest June on Record

By: JeffMasters, 4:11 PM GMT on July 18, 2013

June 2013 was the globe's 5th warmest June since records began in 1880, according to NOAA's National Climatic Data Center (NCDC). NASA rated it the 2nd warmest June on record. The year-to-date period of January - June has been the 7th warmest such period on record. June 2013 global land temperatures were the 3rd warmest on record, and global ocean temperatures were the 10th warmest on record. June 2013 was the 340th consecutive month with global temperatures warmer than the 20th century average. Global satellite-measured temperatures in June 2013 for the lowest 8 km of the atmosphere were 5th or 4th warmest in the 35-year record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH), respectively. Wunderground's weather historian, Christopher C. Burt, has a comprehensive post on the notable weather events of June 2013 in his June 2013 Global Weather Extremes Summary.


Figure 1. Departure of temperature from average for June 2013, the 5th warmest June for the globe since record keeping began in 1880. Record warmth was observed over much of northern Canada, far northwestern Russia, southern Japan, the Philippines, part of southwestern China, and central southern Africa. It was cooler than average across part of central Asia, central India, western Europe, and far northeastern Canada. No record cold was observed over land areas during the month. Image credit: National Climatic Data Center (NCDC) .

Five billion-dollar weather disasters in June
At least five billion-dollar weather disasters hit Earth during June. The most damaging of these was the historic $22 billion flood disaster that killed at least 23 people in Central Europe in late May and early June--the 5th costliest non-U.S. weather disaster in world history. Record flooding unprecedented since the Middle Ages hit major rivers in Austria, the Czech Republic, Germany, Poland and Slovakia; the Danube River in Passau, Germany hit its highest level since 1501, and the Saale River in Halle, Germany was the highest in its 400-year period of record. Numerous cities recorded their highest flood waters in more than a century, although in some locations the great flood of 2002 was higher.

The world-wide tally of billion-dollar weather disasters so far in 2013 is sixteen, and the U.S. total is four, according to the June 2013 Catastrophe Report from insurance broker Aon Benfield:

1) Flooding, Central Europe, 5/30 - 6/6, $22 billion
2) Drought, Brazil, 1/1 - 5/31, $8.3 billion
3) Tornado, Moore, OK, and associated U.S. severe weather, 5/18 - 5/22, $4.5 billion
4) Drought, Central and Eastern China, 1/1 - 4/30, $4.2 billion
5) Flooding, Calgary, Alberta Canada, 6/19 - 6/24, $3.8 billion
6) Flooding, Indonesia, 1/20 - 1/27, $3.31 billion
7) Flooding, Australia, 1/21 - 1/30, $2.5 billion
8) Tornadoes and severe weather, U.S., 5/26 - 6/2, $2 billion
9) Severe weather, Midwest U.S., 3/18 - 3/20, $2 billion
10) Winter weather, Europe, 3/12 - 3/31, $1.8 billion
11) Drought, New Zealand, 1/1 - 5/10, $1.6 billion
12) Flooding, Sichuan Province, China, 7/7 - 7/11, $1.6 billion
13) Flooding, China, 6/29 - 7/3, $1.4 billion
14) Flooding, Argentina, 4/2 - 4/4, $1.3 billion
15) Flooding, India and Nepal, 6/14 - 6/18, $1.1 billion
16) Winter weather, Plains, Midwest, Northeast U.S., 2/24 - 2/27, $1.0 billion

The $8.3 billion cost of the 2013 drought in Brazil makes it by far the costliest natural disaster in Brazil's history, according to the international disasters database EM-DAT. Their 2nd most costly disaster was the drought of 1978 ($2.3 billion in 1978 dollars.)


Figure 2. The Danube River in Passau, Germany hit its highest level since 1501 during the June 2013 flood. Image credit: Stefan Penninger.


Figure 3. The $22 billion price tag of the June - June 2013 Central European floods puts that disaster in 5th place on the list of most expensive non-U.S. weather-related disasters.

Neutral El Niño conditions continue in the equatorial Pacific
For the 15th month in row, neutral El Niño conditions existed in the equatorial Pacific during June 2013. NOAA's Climate Prediction Center (CPC) expects neutral El Niño conditions to last through summer and into the fall, and the large majority of the El Niño models also predict that neutral conditions will last through the fall of 2013. Temperatures in the equatorial Eastern Pacific need to be 0.5°C below average or cooler for three consecutive months for a La Niña episode to be declared; sea surface temperatures were 0.4°C below average as of July 15, and have been +0.1 to -0.4°C from average since April 1, 2013.

Arctic sea ice falls to 11th lowest June extent on record
Arctic sea ice extent during June was 11th lowest in the 35-year satellite record, according to the National Snow and Ice Data Center (NSIDC). The relatively high coverage was due to wind patterns that helped spread the ice out over a larger area. During the first two weeks of July, Arctic ice extent has fallen to the 5th lowest level on record.

Quiet in the Atlantic
There are no tropical cyclone threat areas in the Atlantic to discuss today, and none of the reliable models for tropical cyclone formation is predicting development during the coming seven days. If the Atlantic stays quiet, I plan on making my next post on Saturday.

Jeff Masters

Climate Summaries

Can a Sharknado hit Los Angeles?

By: JeffMasters, 1:38 PM GMT on July 17, 2013

I learned something from watching the movie "Sharknado", SyFy Channel's twisted cross between Jaws, The Day After Tomorrow, and The Texas Chainsaw Massacre, which premiered last Thursday (and will be aired again this Thursday.) My hurricane disaster kit is incomplete without a chainsaw. Not only can a chainsaw come in handy to remove fallen debris after the storm--it can be an essential self-defense weapon in case a hurricane spawns a "Sharknado"--a powerful waterspout that picks up man-eating sharks out of the ocean and hurls them miles inland.



"Sharknado" is set in Los Angeles, where huge and dangerous Hurricane David is making landfall. The satellite images of the hurricane show a very nasty-looking storm that is at least Category 3, but has the rather unusual (and impossible) characteristic that it spins clockwise in the Northern Hemisphere. Thousands of bloodthirsty sharks swarm inland with the hurricane's storm surge and are hurled through the air by the EF-4 waterspouts turned tornadoes that accompany the storm. A lot of blood spurts, a lot of bad acting and lame dialog occur, and plenty of improbable or impossible meteorological events happen--complete with cheesy computer graphic animations. ("Sharknado" seriously challenges The Day After Tomorrow for greatest number of impossible meteorological events packed into a single movie.) But, as long as you don't take the movie too seriously, and look at it as a campy low-budget parody of both disaster movies and horror movies, "Sharknado" is a hoot. I give "Sharknado" two stars (out of four.) The movie is produced by "B" movie studio Asylum, and stars Ian Ziering and Tara Reid. "Sharknado" is airing again at 7pm EDT/6pm CDT on Thursday, July 18, on the SyFy Channel.


Figure 1. Hurricane Linda heads north along the Baja California coast towards towards San Diego on September 12, 1997, as seen by the NOAA GOES-9 satellite. Images and rendering by Marit Jentoft-Nilsen of NASA.

Hurricanes do occur in Southern California
Southern California has been affected by one full-fledged hurricane in recorded history, a Category 1 storm that brought 80 mph winds to San Diego on October 2, 1858. More recently, a 1939 tropical storm brought 52 mph winds to the coast south of Los Angeles, and caused $2 million in property damage--mostly to shipping, shore structures, power and communication lines, and crops. Forty-five lives were lost at sea during the storm. Hurricane Linda of 1997, which occurred during a strong El Niño event that significantly warmed the ocean waters along the Mexican Pacific coast, was forecast by the National Hurricane Center for a couple of advisories to make landfall near San Diego as a minimal hurricane or strong tropical storm. Category 5 Linda was the strongest hurricane ever observed in the Eastern Pacific Ocean, but weakened over cold water and turned out to sea without affecting Southern California. A Category 3 or stronger storm affecting Southern California, as depicted in "Sharknado", is pretty much impossible in the current climate, though. The California Current that flows southwards along the coast of California and Baja Mexico features waters temperatures that are too cold to support a major hurricane.

Falls of fish from the sky
There have been numerous reports of waterspouts or tornadoes picking up fish out of the sea or out of lakes and creating a "rain of fish." For example, hundreds of perch bombarded residents of the small Australian outback town of Lajamanu in 2010. In the U.S., thousands of small fish, frogs and crayfish fell from the sky during a rainstorm at Magnolia Terminal near Thomasville, Alabama, on the morning of June 28, 1957. Many of the fish were alive and were placed in ponds and swimming pools. An F2 tornado fifteen miles to the south spawned by the outer bands of Hurricane Audrey was likely responsible for getting the creatures airborne. William Corliss' intriguing book, "Handbook of Unusual Natural Phenomena", has an entire chapter devoted to unusual creatures and objects that have fallen from the sky. He relates that in 1946, a scientist at the American Museum of Natural History named E. W. Gudger documented 78 reliable reports of fish falls from all over the world. The largest fish was a large-mouthed bass 9 1/4 inches long, and the heaviest was a six pound fish that fell in India. There were no reports of large, 2000-pound great white sharks, as depicted by "Sharknado", though. Wunderground, for now, has decided not to create a new "Sharknado" weather icon for the web site, due to the low probability of such an event occurring with the current laws of physics being what they are.


Video 1. Official trailer for "Sharknado."

Jeff Masters

Book and Movie Reviews

Wet June on the East Coast Raises Hurricane Flood Risk

By: JeffMasters, 1:41 PM GMT on July 16, 2013

June 2013 was the 15th warmest June in the contiguous U.S. since record keeping began in 1895, said NOAA's National Climatic Data Center (NCDC) in their latest State of the Climate report. Six Southwest U.S. states had a top-ten warmest June on record, and no states recorded a significantly below-average June for temperatures. Over three times as many record warm highs and lows occurred than record cold highs and lows during June. For the year-to-date period January - June, both temperature and precipitation over the contiguous U.S. have been above normal, ranking in the upper 33% and 23% of years, respectively.

According to NOAA's U.S. Climate Extremes Index (CEI), which tracks the percentage area of the contiguous U.S. experiencing top-10% and bottom-10% extremes in temperature, precipitation, and drought, June extremes were about 10% below average, and the year-to-date period January - June 2013 has been 20% below average.


Figure 1. Historical temperature ranking for the U.S. for June 2013. Six Southwest U.S. states had a top-ten warmest June on record, and no states recorded a significantly below-average June for temperatures. Image credit: National Climatic Data Center (NCDC).

Wet June on the East Coast raises hurricane flood risk
It was a very June for the contiguous U.S., ranking as the 13th wettest June since 1895. New Jersey and Delaware had their wettest June on record, and sixteen other eastern states had a top-ten wettest June. The very wet June has brought some of the highest soil moisture levels ever recorded for July along much of the coast from Florida to Maine, increasing the chances of extreme flooding should this region receive a hit from a tropical storm or hurricane during the coming peak months of hurricane season. The latest 2-week forecast from the GFS model keeps the East Coast under a wetter-than-average weather pattern into early August, and the latest 1-month and 3-month precipitation outlooks from NOAA's Climate Prediction Center also give above-average chances of wetter than average conditions. Lake Okeechobee in Florida is 1.4' above average for this time of year, and 5' higher than two years ago. While this still puts the lake 1.2' below what is considered high water, Lake Okeechobee water levels will need to be watched as we head into the peak part of hurricane season.


Figure 2. Historical precipitation ranking for the U.S. for June 2013. New Jersey and Delaware had their wettest June on record, and sixteen other eastern states had a top-ten wettest June on record. Utah had its driest June on record, and Arizona, Colorado, and Wyoming had a top-ten driest June. Image credit: National Climatic Data Center (NCDC).


Figure 3. Soil moisture for July 14, 2013, expressed as percent average of the soil moisture observed between 1916 - 2004. Portions of Florida, Georgia, South Carolina, North Carolina, Virginia, Maryland, New York, Vermont, and New Hampshire are near their highest soil moisture levels on record for this time of year, increasing the odds of extreme flooding in those states should a tropical storm or hurricane hit this year. Image credit: University of Washington Variable Infiltration Capacity Macro-scale Hydrological Model, which includes soil moisture, snow water equivalent, and runoff.

Drought conditions remained relatively unchanged during June. According to the July 9 Drought Monitor report, about 45% of the contiguous U.S. is still in moderate or greater drought, compared to 44% at the beginning of June. The U.S. Seasonal Drought Outlook issued on June 21 calls for little overall change in the U.S. area covered by drought conditions during the remainder of summer. Approximately 1.2 million acres of land burned in the U.S. during June, which is above average. However, the year-to-date total acreage burned is the second lowest in the past ten years.

Quiet in the Atlantic
There are no tropical cyclone threat areas in the Atlantic to discuss today, and none of the reliable models for tropical cyclone formation is predicting development during the coming seven days.

Jeff Masters

Climate Summaries

India's June 2013 Flood: Earth's 4th Deadliest Weather Disaster Since 2000

By: JeffMasters, 3:10 PM GMT on July 15, 2013

Over five thousand people missing in the wake of the devastating flooding that hit India's Himalayan Uttarakhand region on June 14 - 17, 2013, have now been declared dead, making the disaster India's deadliest monsoon flood event on record, and Earth's 4th deadliest weather-related disaster since 2000. The death toll of 5,748 tops India's previous record worst monsoon flood death toll of 4892, set in July 1968 in Rajasthan and Gujara provinces. According to the Indian Meteorological Department, Uttarakhand, which lies just to the west of Nepal in the Himalayas, received rainfall 847% of normal during the week June 13 - 19, 2013. Dehradun, the capital of Uttarakhand, received 14.57" (370 mm) of rain in 24 hours on June 16 - 17, the highest 24-hour rainfall in city history. The torrential rains triggered a massive landslide that hit Uttarakhand's Hindu shrine in Kedarnath, which lies just a short distance from the snout of two mountain glaciers. The shrine is an important pilgrimage destination in June, and was packed with visitors celebrating a religious holiday. The June 2013 monsoon rains in Uttarakhand were highly unusual, as the monsoon came to the region two weeks earlier than normal. The monsoon started in South India near the normal June 1 arrival date, but then advanced across India in unusually rapid fashion, arriving in Pakistan along the western border of India on June 16, a full month earlier than normal. This was the fastest progression of the monsoon on record. The previous record for fastest monsoon progression occurred in 1961, when all of India was under monsoon conditions by June 21. Reliable monsoon records go back to 1961. Dr. Dave Petley's Landslide Blog has an excellent analysis of the event. He writes: "The important factor here is that the rainfall fell at a time when there was still snow on the ground--and any high mountain landslide expert will tell you that the combination of heavy rainfall on melting snow is the tailor-made for landslides."


Figure 1. Indo-Tibetan Border Police (ITBP) arrive to rescue stranded Sikh devotees from Hemkunt Sahib Gurudwara, a religious Sikh temple, to a safe place in Chamoli district, in northern Indian state of Uttarakhand, India, Monday, June 17, 2013. AP photo.


Figure 2. Satellite-estimated rainfall for the 7-day period June 11 - 17, 2013, from NASA's TRMM satellite exceeded 20 inches (508 mm) over portions of India's Uttarakhand province, leading to catastrophic floods. Image credit: NASA.

India's 2013 Flood Earth's 4th deadliest weather-related disaster since 2000
This summer's flooding tragedy in India is the globe's fourth-deadliest weather-related disaster since the year 2000, according to EM-DAT, the International Disaster Database. Only Myanmar's Cyclone Nargis in 2008 and heat waves in Europe in 2003 and Russia in 2010 killed more people. However, global flood deaths have not been trending upwards over the past decade. Deaths due to floods and storms declined during the decade of 2001 - 2010, compared to the previous decade. A report issued earlier this month by the World Meteorological Organization titled, 2001-2010, A Decade of Climate Extremes, found that there was a 16% decline in deaths due to storms and 43% decline in deaths from floods, thanks mainly to better early warning systems and increased preparedness and despite an increase in populations in disaster-prone areas. The bad news is that weather-related deaths as a whole increased by 20% during the decade of 2001 - 2010, compared to 1991 - 2000, due to the huge number of deaths from the European heat wave of 2003 and the Russian heat wave of 2010. Less than 6000 people died in heat waves during 1991-2000, compared to 136,000 heat wave deaths in 2001-2010.

Earth's Deadliest Weather-Related Disasters Since 2000
1) Cyclone Nargis, Mayanmar, 2008: 138,366
2) Heat wave, Europe, 2003: 71,310
3) Heat wave, Russia, 2010: 55,736
4) Flood, India, 2013: 5,748
5) Cyclone Sidr, Bangladesh, 2007: 4234
6) Heat wave, Europe, 2006: 3418
7) Hurricane Jeanne, Haiti: 2004, 2754
8) Flood, Haiti, May 2004: 2665
9) Flood, Pakistan, 2010: 1985
10) Typhoon Bopha, Philippines: 2012, 1901
11) Hurricane Katrina, U.S., 2005: 1833
12) Landslide, China, 2010: 1765

Monsoons in India: a primer
Disastrous monsoon floods are common in India and surrounding nations, and 60,000 people have died in floods between 1950 - 2012, according to EM-DAT, the International Disaster Database. EM-DAT lists seventeen flood disasters which killed 1,000 or more people in India since records began in 1950. Here are the number of people killed in these events, along with the month and year of occurrence and locales affected:

5,748, Jun 2013, Uttarakhand
4892, Jul 1968, Rajasthan, Gujara
3800, Jul 1978, North, Northeast
2001, May - Oct, 1994, Assam, Arunachal Pradesh
2000, Jul 1961, North
1811, Aug 1998, Assam, Arunachal, Bihar
1600, Aug 1980, Uttar Pradesh, Bihar
1591, Jul 28, 1989, Maharashtra, Andhra Prade
1479, Sep 1995, Bihar, Haryana, Punjab
1442, Aug 1997, Andhra Pradesh, Arunachal
1200, Jul 24 - Aug 5, 2005 Gujarat, Madhya Pradesh
1200, Aug 1987, Assam, Bihar, West Bengal
1103, Jul 3 - Sep 22, 2007, Bihar, Uttar Pradesh
1063, Jun 11 - Jul 21, 2008 West Bengal, Orissa
1023, Jun 1971, North
1000, Sep 22 - Oct 9, 1988, Punjab, Himachal Pradesh
1000, Sep - Oct 1968
1000, Oct 1961

The monsoon occurs in summer, when the sun warms up land areas more strongly than ocean areas. This happens because wind and ocean turbulence mix the ocean's absorbed heat into a "mixed layer" approximately 50 meters deep, whereas on land, the sun's heat penetrates at a slow rate to a limited depth. Furthermore, due to its molecular properties, water has the ability to absorb more heat than the solid materials that make up land. As a result of this summertime differential heating of land and ocean, a low pressure region featuring rising air develops over land areas. Moisture-laden ocean winds blow towards the low pressure region and are drawn upwards once over land. The rising air expands and cools, condensing its moisture into some of the heaviest rains on Earth--the monsoon. Monsoons operate via the same principle as the familiar summer afternoon sea breeze, but on a grand scale. Each summer, monsoons affect every continent on Earth except Antarctica, and are responsible for life-giving rains that sustain the lives of billions of people. In India, home for over 1.1 billion people, the monsoon provides 80% of the annual rainfall.

Related posts
Over 500 Killed in India's Monsoon Floods, my June 21, 2013 blog post, which discussed the climate change-monsoon connection.

Wunderblogger Lee Grenci's post, Summer Monsoon Advances Rapidly across India: Massive Flooding Ensues, has more detail on the meteorology of this year's monsoon.

Wunderground's climate change blogger Dr. Ricky Rood wrote a nice 3-part series about the challenges India faces due to climate change after he completed a 2009 trip there.


Video 1. Rampaging flood waters at Uttarakhand's Hindu shrine in Kedarnath, India, June 16, 2013.

Jeff Masters

Flood

Canada's 2nd Largest Fire on Record Spreading Smoke to Europe

By: JeffMasters, 2:14 PM GMT on July 13, 2013

A massive fire burning in northern Quebec is Canada's second largest fire since fire records began in 1959, according to the Canadian Forest Service. The fire was more than twice the size of Rhode Island on Tuesday--1,621,000 acres. Called the Eastmain fire, the near-record blaze was ignited by lightning on May 25, and was burning along a 100-km front near the east shore of James Bay by the village of Eastmain. At times, the fire spread at 19 mph (30 kph). The fire cut power to Montreal's subway system and to 10% of the population of Quebec (500,000 customers) on July 4, when smoke from the fire ionized the air by key hydroelectric power lines, causing a cascade failure.


Figure 1. On July 4, 2013, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this image of wildfires burning in western Quebec near James Bay. Red outlines indicate hot spots where MODIS detected unusually warm surface temperatures associated with fire. The Eastmain fire, which became the 2nd largest fire since 1959 in Canada at 1.6 million acres, is at the upper left of the image, just east of James Bay. Other fires near Nemiscau, Quebec (about 150 - 200 km to the southeast of Eastmain) are also burning, but these patches are "only" 120,000 - 200,000 acres. MODIS also observed smoke from the fires moving across the Atlantic Ocean on July 5, July 6, and July 7. By July 8, smoke was drifting over Scandinavia. Image credit: NASA.

The largest fire in Canadian history was the 2,119,000 acre fire that burned in 1979 in the Northwest Territories. For comparison, the total acreage burned by wildfires in the U.S. as of July 4, 2013 was 1.9 million acres, so the Eastmain fire by itself has burned almost as large an area. The fire's spread is being limited by the Opinaca Reservoir on its east, and by areas burned in 2002 to the south. The fire spread rapidly last week into a patch along its northern and northeastern sides that burned in 1989 (click hereto see the very impressive spread of the fire between 16:45 UTC and 18:22 UTC last Thursday from the Suomi NPP VIIRS shortwave IR instrument; look on the northeastern front of the fire, which is inside the former 1989 fire patch--it spreads extraordinarily rapidly at approximately 10 mph.) While cool and relatively wet weather is expected in Quebec during the coming week, keeping fire danger low, there is speculation by some Canadian fire experts that the Eastmain fire will burn the entire summer unless there are a significant number of consecutive rainy days.


Figure 2. Dr. Jason Box extracts a core sample from the Greenland Ice Sheet on July 9, 2013, during the DarkSnow Project. The core will be analyzed to determine if smoke from wildfires is contributing to melting of the ice sheet by darkening it.

Canadian fire smoke reaches Europe
Smoke from this summer's fires in Quebec have crossed the Atlantic and reached Scandanavia, according to ScienceDaily.com. The smoke also passed over Greenland when the crowd source-funded DarkSnow Project was taking samples of the Greenland ice. The DarkSnow Project was designed to see if forest fires are significantly darkening the Greenland Ice Sheet, contributing to melt.

Climate change and fire suppression in Canada
Fire suppression policies are different in Canada than in the U.S. In areas where these fire are burning, there is no direct fire suppression unless fire is near villages and hydroelectric facilities. Nevertheless, fire suppression costs $500 million per year in Canada. "In areas with high timber or other values, a full fire-suppression response is used in attempts to control fires as quickly as possible. In areas with low values at risk to fire, a modified fire-suppression response, which attempts to control fires in a limited way, is usually used: isolated values threatened by fire are protected, or the fire is simply monitored. While only 5% of the fires detected during 1990–2004 received a modified response, they accounted for about 60% of the area burned " (Hirsch et al., 2006.)
 
Fire suppression efficiency depends on many factors, including fire danger, the size at which the fire is attacked, and the number of fires already burning. According to Cummings (2005) and Martell and Sun (2008), fire suppression can significantly reduce area burned in boreal forests. Fire suppression can reduce area burned by means of initial attack, which reduces the number of large fires. Consequently, fire suppression agencies are efficient when the fire danger is low and when there is not that much fire already burning, a situation that will be less common in the near future. For Ontario, Podur and Wotton (2010) projected "a doubling of area burned in the Intensive and Measured fire management zones of Ontario by the decade of 2040, and an eightfold increase in area burned by the end of the 21st century" due to climate change (IPCC A2 scenario.) Fires that are too intense to control will overwhelm the fire management system and cause major increases in area burned.

Another study (Boulanger et al. 2013) predicted for 2040 in eastern Canada a 2.2- and 2.4-fold increase in the number of fires and the annual area burned, respectively, mostly as a result of an increase in extreme fire-weather normals and drought. As extreme fire danger would occur later in the fire season on average, the fire season would shift slightly later (5–20 days) in the summer. However, if broadleaf species become more common in this area as a result of climate change, this may offset the climate change impact on drought, as broadleaf trees are less flammable than coniferous trees (Girardin et al. 2013).


Video 1. Maxime Duperré, traveling in a truck near Nemiscau, Quebec, took this video of one of the massive fires burning in Quebec this July.

References
 Boulanger, Y., Gauthier, S., Gray, D. R., Le Goff, H., Lefort, P., Morissette, J. 2013. Fire regime zonation under curent and future climate over eastern Canada. Ecol. Appl. 23: 904-923. 
 
Cumming, S.G. 2005. Effective fire suppression in the boreal forests. Can. J. For. Res. 35: 772-786.
 
Girardin, M.P., Ali, A. A., Carcaillet, C., Blarquez, O., Hély, C., Terrier, A., Genries, A., Bergeron, Y. 2013. Vegetation limits the impact of a warm climate on boreal wildfires. New Phytologist (In Press).
 
Hirsch, K.G.; Fuglem, P., Technical Coordinators. 2006. Canadian Wildland Fire Strategy: background syntheses, analyses, and perspectives. Can. Counc. For. Minist., Nat. Resour. Can., Can. For. Serv., North. For. Cent., Edmonton, AB.
 
Martell, D. and Sun, H. 2008. The impact of fire suppression, vegetation, and weather on the area burned by lightning-caused fires in Ontario. Can. J. For. Res. 38:1547-1563.
 
D. Podur, J. and Wotton, B. M. 2010. Will climate change overwhelm fire management capacity ? Ecological Modelling 221:1301-1309

A tough year for natural disasters in Canada
This summer's huge fires in Quebec have been caused by what is being called the driest summer in 40 years in the James Bay region. However, other portions of Canada have received record rains that have triggered two of the most damaging floods in Canadian history. The first of these floods hit Calgary, Alberta in mid-June, causing $3.8 billion in damage--the most expensive flood ever to hit Canada, and the second most expensive natural disaster of any kind. And on July 8, Toronto was hit with its heaviest 1-day rainfall on record, with a preliminary damage estimate by an official from the Insurance Bureau of Canada of $600 million, which would make it the 4th costliest flood in Canadian history. Here are the top five most damaging floods in Canada, with the non-bold faced entries taken from EM-DAT (unadjusted for inflation):

1) $3.8 billion, June 2013, Calgary, Alberta
2) $0.8 billion, May 2011, St. Andrew, Manitoba
3) $0.7 billion, July 1996, Saguenay-Lac-Saint-Jean region, Quebec
4) $0.6 billion, July 2013, Toronto, Ontario
5) $0.4 billion, June 2005, Alberta

The Atlantic is quiet
The Atlantic is relatively quiet. A small non-tropical area of low pressure is developing near the coast of Alabama along a stalled-out cold front, and the remains of Chantal are moving northwards towards the North Carolina coast. Neither of these areas appears to be of concern, and in their 8 am EDT Saturday Tropical Weather Outlook, NHC gave both of these areas a 10% chance of development into a tropical depression or tropical storm by Monday. None of the reliable computer models are predicting development of of anything in the Atlantic over the next seven days. If conditions remain quiet, my next post will be on Monday.

Jeff Masters

Fire

Ex-Chantal Unlikely to Develop; Typhoon Soulik Pounding Taiwan

By: JeffMasters, 1:42 PM GMT on July 12, 2013

The remains of Tropical Storm Chantal are bringing heavy rains and gusty winds to the Northwest Bahama Islands today, as the storm slides northwards at 10 mph. However, the storm is poorly organized with only a modest amount of heavy thunderstorm activity, and today's hurricane hunter mission into ex-Chantal has been cancelled. Before it dissipated on Wednesday, Chantal brought heavy rains to Haiti and the Dominican Republic, with satellite estimates of 4 - 8 inches of rainfall in Central Haiti and the central and south coastal Dominican Republic. One drowning death in the Dominican Republic is being blamed on the storm.


Figure 1. Satellite image of Chantal's remains over the Bahamas, taken at 9 am EDT Friday, July 12, 2013. Note also the clouds at the upper left of the image, associated with a stalled-out cold front over coastal South Carolina. Image credit: NASA/GSFC.

Forecast for Chantal's remains
The remains of Chantal will spread northwards into the offshore waters of South Carolina and North Carolina on Saturday and Sunday, and will contribute moisture to a stalled front expected to bring 2 - 3" of rain to the coast. Moderate wind shear of 10 - 20 knots is expected to affect the storm through Saturday, so some re-organization is possible. However, given its current disorganized state, it is unlikely that ex-Chantal will become a tropical depression or tropical storm again. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave Chantal's remains a 10% chance of development into a tropical depression or tropical storm by Sunday. None of the reliable computer models are predicting development of Chantal's remains, or of anything else in the Atlantic over the next seven days.


Figure 2. Radar image of Typhoon Soulik approaching Taiwan, taken at 9 pm local time on July 12, 2013. Image credit: Central Weather Bureau, Taiwan.

Typhoon Soulik closes in on Taiwan
Heavy rains are lashing Taiwan as Typhoon Soulik, a Category 2 storm with 105 mph winds in the Western Pacific, approaches landfall. At 9 pm local time on Friday, Ishigakijima, Japan, on an island in the northern eyewall of Soulik, recorded sustained 10-minute winds of 80 mph. Soulik is expected to hit the northern end of Taiwan on Friday near 8 pm EDT as a Category 2 storm. Soulik will then make landfall in China near Fuzhou on Saturday at around 6 am EDT, most likely as a Category 1 typhoon. Soulik became the most powerful tropical cyclone of 2013 on Wednesday, when it peaked at Category 4 strength with 145 mph winds.

Taiwan's typhoon history
Taiwan was hit by two typhoons in 2012, Typhoon Tembin (eight killed, $8 million in damage) and Typhoon Saola (six killed, $27 million in damage.) Almost 70 inches fell in some areas of Taiwan, ranking Saola within the top five wettest cyclones to ever hit the island. According to EMDAT, the most expensive typhoon in Taiwan's history was 2009's Typhoon Morakot ($2.3 billion in damage.) The Category 1 storm dumped the most rain by a typhoon ever recorded in Taiwan, up to 2,777 mm (109.3".) The devastating flooding that resulted killed 630 people, making it the 4th deadliest typhoon in Taiwanese history. The deadliest typhoon in Taiwan's history was Category 3 Typhoon Ellen of 1959, which dumped 25 inches (640 mm) of rain in one day (August 7) on the mountains and western plains, triggering catastrophic flooding that killed 1046 people.


Video 1. Demo of the new WunderMap app.

Wunderground releases its WunderMap application for Android tablets and iPad
Weather Underground is pleased to announce the release of its new WunderMap® application for both Android and iOS tablets. This new touch screen version of WunderMap provides access to Weather Underground's unique community of neighborhood weather stations and webcams, as well as animated radar and satellite, hurricane tracking tools, wildfire layers, and much more.

With the WunderMap app, users can tap into one of the 30,000+ personal weather stations to see hyper-local weather conditions and forecasts, track a storm in real-time, and customize a variety of weather layers to access the most relevant weather information. WunderMap® is a fully interactive experience that allows users to customize the weather data plotted on the Google Map interface--making it relevant for both the savvy storm tracker or the casual weather user on the go.

WunderMap and the touch-screen device are a perfect match. Being able to swipe across the world and zoom in to see our hyper-local weather within such an interactive user interface makes WunderMap a unique way to access weather information. Other features of the app include:

- Current conditions, extended forecasts, and weather graphs for every location
- Special weather statements and advisories
- Customizable location presets and favorites
- Enhanced animation options
- Advanced search functionality
- New map interface options
- Free to download in the Google Play or iTunes Store
-Ad-free membership upgrade available for $1.99

You can download the app at www.wundermap.com.

Jeff Masters

Hurricane

Chantal Dissipates; its Remains Bringing Heavy Rains to the Bahamas

By: JeffMasters, 1:28 PM GMT on July 11, 2013

The remains of Tropical Storm Chantal are bringing heavy rains and gusty winds to the Southeast Bahamas and Turks and Caicos Islands today, after the storm dissipated on Wednesday approaching Haiti. Chantal brought heavy rains to Haiti and the Dominican Republic on Wednesday, with satellite estimates of 4 - 8 inches of rainfall in Central Haiti and the central and south coastal Dominican Republic. One drowning death in the Dominican Republic is being blamed on the storm.


Figure 1. Predicted precipitation for the 7-day period ending Thursday, July 18, 2013. Chantal's remains are expected to bring 2 - 3" of rain to the Southeast U.S., which will not be great enough to cause major flooding issues. Image credit: NOAA/HPC.

Forecast for Chantal's remains
The remains of Chantal will spread into the Northwest Bahamas on Friday, and to the Southeast U.S. on Saturday and Sunday. High wind shear of 20 - 30 knots combined with dry air will make re-development of the storm unlikely through Friday. On Saturday, the wind shear over Chantal's remains will fall to the moderate range, but the storm will likely not have enough time over water to redevelop. In their 8 am EDT Tropical Weather Outlook, NHC gave Chantal's remains a 20% chance of development into a tropical depression or tropical storm by Saturday. None of the reliable computer models are predicting development of Chantal's remains, or of anything else in the Atlantic over the next seven days.


Figure 2. MODIS image of Typhoon Soulik taken at 04:20 UTC July 11, 2013. Image credit: NASA.

Typhoon Soulik a threat to Taiwan and China
Typhoon Soulik, a Category 2 storm with 110 mph winds in the Western Pacific, is expected to hit the northern end of Taiwan on Friday as a Category 3 storm. Soulik will then make landfall in China near Fuzhou on Saturday, most likely as a Category 2 typhoon. Soulik became the most powerful tropical cyclone of 2013 on Wednesday, when it peaked at Category 4 strength with 145 mph winds.

Jeff Masters

Hurricane

Chantal Barely Alive, Bringing Heavy Rains to Haiti and the Dominican Republic

By: JeffMasters, 3:24 PM GMT on July 10, 2013

An Air Force hurricane hunter aircraft criss-crossing Tropical Storm Chantal this morning was barely able to find a closed circulation, and measured top winds of 45 mph at 10:10 am EDT in a region of heavy thunderstorms just south of the Central Dominican Republic coast. High wind shear of 20 - 30 knots, combined with dry air and the storm's exceptionally fast forward movement of 25 - 30 mph have seriously weakened Chantal, even before it has encountered the high mountains of Hispaniola and Cuba. Visible satellite loops show that Chantal has a modest area of heavy thunderstorms that are affecting Haiti and the Dominican Republic. Chantal's rains are a serious threat for Haiti, where deforestation of the nation's mountainous hillsides has left the nation highly vulnerable to flooding. In mid-June, heavy rains in Haiti triggered flash floods that killed at least six people and impacted 7,000 families. In October 2012, flooding from Hurricane Sandy killed 60 people and damaged or destroyed more than 18,000 homes. Drought conditions this year over the nation have left the soil hard and impervious, increasing the risk of rapid run-off from heavy rains. Approximately 320,000 people live in makeshift tent shelters in Haiti, three years after the devastating January 2010 earthquake that killed 220,000 people.


Figure 1. Latest satellite image of Chantal.

Forecast for Chantal
The 8 am EDT Wednesday wind shear forecast from the SHIPS model calls for shear to remain in the high range, 20 - 35 knots, into Thursday. This high shear, combined with Chantal's expected passage over the high mountains of Cuba and the continued presence of dry air, will likely destroy the storm by Friday. Wind shear will likely fall to the moderate range once Chantal moves north of Cuba, so there will be the possibility of regeneration in the waters off the coast of Florida if Chantal does dissipate.

Elsewhere in the Atlantic, none of the reliable forecast models are predicting formation of a tropical cyclone for the coming seven days.


Figure 2. Departure of precipitation from average for the past two weeks over the Southeast U.S. shows many areas have received over 400% of their normal precipitation. Image credit: NOAA/HPC.


Figure 3. Soil moisture over the U.S. on July 8, 2013, ranked as a percentage of the greatest moisture levels on record for the date. Large areas of the Southeast U.S. are near the wettest levels ever observed, above the 99th percentile in soil moisture. Image credit: NOAA/CPC.

Southeast U.S. vulnerable to flooding
If Chantal or its remnants brings heavy rains to the Southeast U.S. early next week, as some of the current track models are predicting, the storm could cause major damaging flooding. The soils in the Southeast are saturated and many rivers are already in flood, due to last week's extreme jet stream pattern that set up a fire hose of tropical moisture that streamed inland from the Florida Panhandle through Georgia, South Carolina, and North Carolina. Soils over large areas of the Southeast U.S. are near the wettest levels ever observed for this time of year--above the 99th percentile in recorded history. It's remarkable that most of Georgia, South Carolina, and North Carolina were in moderate or greater drought at the beginning of the year. Portions of Central Georgia were in exceptional drought--the most extreme category of drought.


Figure 4. MODIS image of Typhoon Soulik taken at 02:10 UTC July 10, 2013. Image credit: NASA.

Powerful Typhoon Soulik a threat to Taiwan and China
Earth's most powerful tropical cyclone so far in 2013 is Typhoon Soulik, a Category 4 storm with 140 mph winds in the Western Pacific. Soulik has weakened slightly from its peak winds of 145 mph earlier today, but is expected to maintain Category 4 strength into Thursday, then weaken to Category 3 strength under the influence of high wind shear of 20 - 25 knots, before hitting the northern end of Taiwan on Friday. Soulik will then make landfall in China near Fuzhou on Saturday, most likely as a Category 1 typhoon. Soulik is the third Category 4 storm globally so far in 2013 (joining January's Tropical Cyclone Narelle and Tropical Cyclone Felleng in the Southern Indian Ocean.) Earth has not yet seen any Category 5 storms in 2013.

Jeff Masters

Hurricane

Unusual Chantal Disorganized, but has 65 mph Winds

By: JeffMasters, 8:06 PM GMT on July 09, 2013

Unusual Tropical Storm Chantal has strengthened a bit more as it speeds west-northwestwards at 26 mph away from the the Lesser Antilles Islands. Sustained winds of 38 mph, gusting to 52 mph, were observed at Martinique at 10 am AST as the storm passed. However, an automated weather station at the airport measured sustained winds of 60 mph, gusting to 78 mph, according to an official with Meteo-France. The Associated Press reported that Chantal ripped the roofs off of several homes on neighboring Dominica. An Air Force hurricane hunter aircraft measured top winds at their 1,000' flight level of 89 mph at 12:55 pm AST. Top winds seen by the aircraft's SFMR instrument were about 65 mph, in a small area east of Chantal's center. The Hurricane Hunters have departed Chantal, and the next plane is due in the storm at 8 pm EDT. Chantal's winds are unusually high considering the storm's high central pressure of 1006 mb and disorganized appearance on satellite imagery. Chantal is fighting dry air associated with the Saharan Air Layer (SAL), as seen on water vapor satellite loops. This dry air is creating strong thunderstorm downdrafts that are robbing Chantal of moisture and energy. Visible satellite loops show the outflow boundaries of these thunderstorm downdrafts at the surface, spreading to the northwest of Chantal. Martinique Radar shows a large area of heavy rain that is not well-organized, lying mostly to the west of the Lesser Antilles Islands.


Figure 1. MODIS image of Chantal taken at approximately 1 pm EDT Tuesday, July 9, 2013. At the time, Chantal had top winds of 65 mph, but looked very disorganized, due to high wind shear and dry air. Dry air is creating strong thunderstorm downdrafts that are robbing Chantal of moisture and energy. Outflow boundaries from these downdrafts are spreading out to the northwest of Chantal, as seen on this satellite image. Image credit: NASA.

An small-scale easterly jet creating high shear in Chantal
Chantal is not very impressive on satellite images, with a modest amount of heavy thunderstorms that are not well-organized. Only a small amount of upper-level outflow is visible. The reason for Chantal's rather disorganized appearance can be found by looking at this morning's balloon sounding from Guadaloupe. This island was just northwest of the center of Chantal when the balloon was launched at 8 am EDT. The sounding showed typical easterly trade winds at the surface of 12 knots (14 mph.) However, the winds rose quickly aloft, with a jet of easterly winds of 35 - 53 knots between 800 - 600 mb (about 7,000 - 15,000'.) But, by the time the ballon hit 500 mb (18,000'), the winds had died down to 15 knots. A change of wind speed from 12 knots to 53 knots and back down to 15 knots from the surface to 500 mb is a tremendous amount of wind shear, which will make it very difficult for a tropical storm to keep the surface center aligned with the upper level center. The traditional measure of wind shear, the difference in wind between 200 mb and 850 mb, was 44 knots in this morning's Guadaloupe sounding, but was a much higher 56 knots from 200 mb to 700 mb. The powerful easterly wind jet was not apparent at any of the other balloon soundings this morning at adjacent islands (Barbados, Puerto Rico, Saint Martin), and demonstrates that there is a lot going on the atmosphere at small scales we cannot see which makes intensity forecasting of tropical cyclones very challenging. Thanks go to Jason Dunion of NOAA's Hurricane Research Division for pointing out this morning's interesting Guadaloupe sounding.

Forecast for Chantal
Chantal will have difficulty intensifying much more before hitting Hispaniola on Wednesday afternoon. In their 11 am EDT wind probability forecast, NHC gave Chantal a 29% chance of becoming a hurricane before hitting Hispaniola. Working against intensification will be the high wind shear from the strong mid-level easterly jet discussed above, plus the fast forward speed of the storm--tropical storms moving faster than 20 mph in the deep tropics usually have trouble intensifying. In addition, the Eastern Caribbean is an area where the trade winds accelerate, helping drive sinking air that discourages tropical storm intensification. Dry air will also slow down the intensification process. Interaction with the high mountains of Hispaniola and high wind shear may be able to destroy Chantal by Thursday. The 2 pm EDT Tuesday wind shear forecast from the SHIPS model calls for shear to rise to the high range, 20 - 35 knots, Tuesday night through Friday. On Saturday, when Chantal is expected to be in the Bahamas, moderate wind shear of 10 - 20 knots is predicted. If Chantal survives until Saturday, it will then have the opportunity to re-strengthen. The latest 12Z run of the European model (ECMWF) dissipates Chantal as it crosses Hispaniola. The 12Z run of the American GFS model has Chantal barely surviving.

Chantal's fast west-northwest forward speed of 26 mph will slow to 20 mph by Wednesday morning and then 10 mph by Thursday night, as the storm "feels" the presence of a trough of low pressure over the U.S. East Coast. This trough will steer Chantal to the northwest and then north-northwest across Hispaniola and into the Bahamas. The trough of low pressure pulling Chantal northwards is expected to lift out the the northeast over the weekend, leaving Chantal behind off the coast of Florida. High pressure will likely build in, potentially forcing Chantal westwards into the Florida or Southeast U.S. coast, with a possible Sunday landfall.

Jeff Masters

Hurricane

Toronto Deluged With its All-Time Record 1-Day Rainfall

By: JeffMasters, 4:20 PM GMT on July 09, 2013

Torrential rains from a series of "training" thunderstorms that moved over the same location brought Toronto, Canada its heaviest 1-day rainfall in recorded history on Monday, July 8. Toronto's Pearson Airport recorded 126 mm (4.96") of rain, beating Toronto's previous all-time rainiest day record set on October 15, 1954, from the remnants of Hurricane Hazel, when 121.4 mm (4.78") fell. Weather records at the airport go back to 1937. According to meteorologist Rob Davis with the Weather Network, the 97 mm (3.82") that fell in downtown Toronto yesterday was the 2nd greatest 1-day rainfall since 1840. The only greater amount fell on July 27, 1897. Yesterday's storms knocked out power to over 300,000 customers in the city and crippled transportation.


Figure 1. Cars stranded on the #DVP, one of Toronto's busiest highways on Monday, July 8, 2013. Photo posted to Twitter by Michelle Shephard@shephardm.


Figure 2. Radar image taken at the height of Toronto's day of record rain on July 8, 2013, showing a line of heavy thunderstorms to the northwest of the city about to move to the southeast over Toronto, bringing several hours of heavy rain.

Canada has taken a beating from extreme weather this year. Less than a month ago, massive flooding hit the city of Calgary, Alberta, creating a $3 billion flood disaster. This was the most expensive flood in Canadian history, and third most expensive natural disaster of any kind for the country. The only more expensive disasters were a 1989 wildfire ($4.2 billion in 1989 dollars) and a 1977 drought ($3 billion in 1977 dollars.) It's also been a bad fire season in Canada. According to an email I received from Yan Boulanger of Ressources Naturelles Canada, Canadian Forest Service, a fire that has consumed about 500,00 hectares (1,235,000 acres) in Eastmain, Quebec is the biggest fire in Quebec's recent history, from 1959 onward.

Some rather remarkable Toronto flooding photos are posted at the Weather Network.

Jeff Masters

Flood

Chantal Strengthening as it Plows Through the Lesser Antilles Islands

By: JeffMasters, 1:41 PM GMT on July 09, 2013

Tropical Storm Chantal is strengthening as it speeds west-northwestwards at 26 mph through the Lesser Antilles Islands. At 6:22 am AST, St. Lucia recorded a wind gust of 54 mph. Sustained winds of 38 mph, gusting to 52 mph, were observed at Martinique at 10 am AST. An Air Force hurricane hunter aircraft is in the storm, and measured top winds at their 1,000' flight level of 80 mph at 8:41 am AST, about 20 miles north of the center. Top winds seen by the aircraft's SFMR instrument were about 60 mph, and it is likely that NHC will bump up Chantal's top winds to at least 60 mph in their 11 am advisory. Barbados Radar shows a large area of heavy rain that has organized moderately well into low-level spiral bands affecting much of the central Lesser Antilles Islands. Chantal is not very impressive on satellite loops, though, with only a modest amount of heavy thunderstorms that are not well-organized. Only a small amount of upper-level outflow is visible. Chantal is fighting dry air associated with the Saharan Air Layer (SAL), as seen on water vapor satellite loops. Moderate wind shear of 15 - 20 knots is driving dry air into the storm. Ocean temperatures are fairly warm, at 28°C.


Figure 1. Latest satellite image of Chantal.


Figure 2. Barbados weather radar image of Chantal taken at 9:14 am AST on Tuesday, July 9, 2013. Chantal's center was located between St. Lucia and Martinique. Image credit: Barbados Met Service.

Forecast for Chantal
Chantal will likely continue to intensify before hitting Hispaniola on Wednesday afternoon. In their 5 am EDT wind probability forecast, NHC gave Chantal a 23% chance of becoming a hurricane before hitting Hispaniola. Working against intensification will be the fast forward speed of the storm--tropical storms moving faster than 20 mph in the deep tropics usually have trouble intensifying. In addition, the Eastern Caribbean is an area where the trade winds accelerate, helping drive sinking air that discourages tropical storm intensification. Dry air will also slow down the intensification process. Interaction with the high mountains of Hispaniola and high wind shear may be able to destroy Chantal by Thursday. The 8 am EDT Tuesday wind shear forecast from the SHIPS model calls for shear to rise to the high range, 20 - 30 knots, as the storm approaches and crosses Hispaniola on Wednesday and Thursday. On Friday and Saturday, when Chantal is expected to be in the Bahamas, lower moderate wind shear of 15 - 20 knots should allow for re-intensification of the storm--if it survives interaction with the high mountains of Hispaniola, Puerto Rico, and Eastern Cuba. The latest 06Z run of the GFS model dissipates Chantal as it crosses Hispaniola, though the 00Z run done 6 hours earlier had the storm surviving. Chantal has the potential to cause big problems for Haiti, which is highly vulnerable to flash flooding due to the lack of vegetation on the deforested mountains. However, there is a lot of dry air to the west of Chantal, which may act to keep rainfall totals in Haiti down to a manageable 2 - 4". Over 300,000 people are still homeless and living in makeshift tent camps in Haiti, three years after the great 2010 earthquake.

Chantal's fast west-northwest forward speed of 26 mph will slow to 20 mph by Wednesday afternoon and then 10 mph by Thursday afternoon, as the storm "feels" the presence of a trough of low pressure over the U.S. East Coast. This trough will steer Chantal to the northwest and then north-northwest across Hispaniola and into the Bahamas. The trough of low pressure pulling Chantal northwards is expected to lift out the the northeast over the weekend, leaving Chantal behind off the coast of Florida. High pressure will likely build in, potentially forcing an intensifying Chantal westwards into the Florida or Southeast U.S. coast, with a possible Monday landfall.

Jeff Masters

Hurricane

Tropical Storm Chantal: a Likely Harbinger of an Active Atlantic Hurricane Season

By: JeffMasters, 2:02 PM GMT on July 08, 2013

Tropical Storm Chantal is speeding westwards at 26 mph towards a Tuesday encounter with the Lesser Antilles Islands. Satellite loops show that Chantal has plenty of spin, with several well-developed low-level spiral bands that have gradually increased their heavy thunderstorm activity this morning. However, Chantal is fighting dry air associated with the Saharan Air Layer (SAL). The heavy thunderstorm activity near Chantal's center is rather thin, and there are virtually no heavy thunderstorms on the storm's north side, where upper-level northwesterly winds are creating light to moderate wind shear of 5 - 15 knots, and driving dry air into the storm. This dry air is readily apparent on water vapor satellite loops. Ocean temperatures are fairly warm, though, at 27.5 - 28°C. There have not been any hurricane hunter missions into Chantal yet, but an Air Force hurricane hunter aircraft deployed to St. Croix on Sunday, and is scheduled to investigate Chantal on Monday afternoon.


Figure 1. MODIS image of Chantal taken at approximately 10 am EDT Monday, July 8, 2013. At the time, Chantal had top winds of 45 mph. Image credit: NASA.


Figure 2. U.S. Air Force Master Sgt. Levi Denham, a WC-130J Hercules aircraft weather reconnaissance loadmaster assigned to the 53rd Reconnaissance Squadron (the Hurricane Hunters), performs pre-engine start-up inspections in St. Croix, Virgin Islands, on Sept. 16, 2010. DoD photo by Staff Sgt. Manuel J. Martinez, U.S. Air Force. Thanks go to wunderground member Patrap for pointing out this photo.

Forecast for Chantal
The 8 am EDT Monday forecast from the SHIPS model predicts that Chantal will experience low to moderate shear through Tuesday afternoon as it heads west-northwest at 25 mph towards Hispaniola. With ocean temperatures expected to warm to 28°C during that time, Chantal has the potential to intensify to a 65 mph tropical storm before hitting Hispaniola. Working against intensification will be the fast forward speed of the storm--tropical storms moving faster than 20 mph in the deep tropics usually have trouble intensifying. In addition, the Eastern Caribbean is an area where the trade winds accelerate, helping drive sinking air that discourages tropical storm intensification. Dry air will also slow down the intensification process, and I don't see Chantal making it to hurricane strength before interacting with the mountains of Hispaniola and/or Cuba on Tuesday night and Wednesday. This interaction may be able to destroy the storm, since wind shear is also expected to rise to the high range, 20 - 30 knots, Tuesday night through Thursday. Chantal has the potential to cause big problems for Haiti, which is highly vulnerable to flash flooding due to the lack of vegetation on the deforested mountains. However, there is a lot of dry air to the west of Chantal, which may act to keep rainfall totals in Haiti down to a manageable 2 - 4". Over 300,000 people are still homeless and living in makeshift tent camps in Haiti, three years after the great 2010 earthquake.

Once Chantal crosses Hispaniola and enters the Bahamas late this week, the trough of low pressure pulling the storm to the northwest is expected to lift out. It is unclear at this point whether or not this trough will be strong enough to pull Chantal out to sea, or whether the storm might be forced back to the northwest into the U.S. East Coast by high pressure building in.


Figure 3. There have been only thirteen tropical depressions or tropical storms that have formed July 15 or earlier that have passed through the Lesser Antilles since 1851, an average of one such tropical cyclone every thirteen years. Note that two of these storms, Dennis and Emily, occurred during the notorious Hurricane Season of 2005. There were five other pre-July 16 storms that formed east of the Lesser Antilles Islands, but did not pass through the islands (Bertha of 2009, Barry of 1989, and unnamed tropical depressions in 1967, 1978, and 2001.) Image credit: NOAA's Historical Hurricane Tracks website.

Chantal: an uncommon early-season Cape Verde-type tropical storm
Formation of a tropical storm east of the Lesser Antilles Islands in early July from an African tropical wave is an uncommon occurrence. Since Atlantic hurricane records began in 1851, there have been only thirteen tropical depressions or tropical storms that have formed July 15 or earlier that have passed through the Lesser Antilles, an average of one early-season tropical cyclone every thirteen years. Note that two of these storms, Dennis and Emily, occurred during the notorious Hurricane Season of 2005. There were five other pre-July 16 storms that formed east of the Lesser Antilles Islands, but did not pass through the islands (Bertha of 2009, Barry of 1989, and tropical depressions in 1967, 1978, and 2001 that did not become named storms.)

Chantal: a likely harbinger of an active Atlantic hurricane season
Chantal's formation on July 8 is an usually early date for formation of the season's third storm, which usually occurs on August 13. A large number of early-season named storms is not necessarily a harbinger of an active season, unless one or more of these storms form in the deep tropics, south of 23.5°N. According to Phil Klotzbach and Bill Gray, leaders of Colorado State's seasonal hurricane forecasting team,

"Most years do not have named storm formations in June and July in the tropical Atlantic (south of 23.5°N); however, if tropical formations do occur, it indicates that a very active hurricane season is likely. For example, the seven years with the most named storm days in the deep tropics in June and July (since 1949) are 1966, 1969, 1995, 1996, 1998, 2005, and 2008. All seven of these seasons were very active. When storms form in the deep tropics in the early part of the hurricane season, it indicates that conditions are already very favorable for TC development. In general, the start of the hurricane season is restricted by thermodynamics (warm SSTs, unstable lapse rates), and therefore deep tropical activity early in the hurricane season implies that the thermodynamics are already quite favorable for tropical cyclone (TC) development."

Two of this season's three storms have formed in the deep tropics--Tropical Storm Barry, which formed in the Gulf of Mexico's Bay of Campeche at a latitude of 19.6°N, and now Tropical Storm Chantal, which formed at a latitude of 9.8°N. With recent runs of the GFS model predicting formation of yet another tropical storm southwest of the Cape Verde Islands early next week, it appears that the Atlantic is primed for an active hurricane season in 2013.

Jeff Masters

Hurricane

95L Near Tropical Depression Status, Headed Towards Lesser Antilles

By: JeffMasters, 4:39 PM GMT on July 07, 2013

A strong and unusually well-organized tropical wave for so early in the season (95L) is speeding westwards at 20 - 25 mph over the Central Atlantic. At noon EDT on Sunday, 95L was near 9.5°N, 43°W, about 1200 miles east of the Lesser Antilles Islands. Satellite loops show that 95L has a well-developed surface circulation center that is exposed to view, with a modest clump of heavy thunderstorms on the south side of the center. The system has several well-developed low-level spiral bands, but is fighting dry air associated with the Saharan Air Layer (SAL). July African tropical waves typically have considerable trouble getting organized in the very dry air of the SAL, and the only factor keeping 95L from currently being classified as a tropical depression is the relative lack of persistent heavy thunderstorm activity near the center of the storm due to dry air. This dry air is readily apparent on water vapor satellite loops. However, the latest SAL analysis (Figure 2) from the University of Wisconsin's SSEC group shows that 95L has moistened the air around it sufficiently to keep the SAL somewhat at bay. An 11:12 am EDT pass by the ASCAT satellite showed top winds of 45 mph on the west side of 95L's center of circulation. ASCAT did not show a closed circulation at the time. Wind shear is light to moderate, 5 - 15 knots, and ocean temperatures are warm, 27.5 - 28°C. An Air Force hurricane hunter aircraft is on call to investigate 95L on Monday afternoon.


Figure 1. MODIS image of 95L taken at approximately 10 am EDT Sunday, July 7, 2013. Image credit: NASA.


Figure 2. Analysis of the Saharan Air Layer (SAL) from 11 am EDT Sunday, July 7, 2013, shows that 95L has walled itself off from the western edge of the SAL. A new tropical wave that has emerged from the coast of Africa is visible on the right of the image. This wave will need to be watched for development late this week, but is farther north than 95L, and may have trouble with dry air as it moves westward across the Atlantic. Image credit: University of Wisconsin SSEC.

Forecast for 95L
The 8 am EDT Sunday forecast from the SHIPS model predicted that 95L would experience low to moderate shear through Tuesday morning as it headed west to west-northwest at 20 - 25 mph. The disturbance should arrive in the Lesser Antilles Islands on Tuesday, and affect the Dominican Republic by Wednesday night. A band a strong upper-level winds associated with the subtropical jet stream is expected to be over the northern islands this week, and as soon as 95L penetrates as far north as 15°N latitude, it will encounter high wind shear of 20 - 30 knots. But if 95L stays farther to the south, wind shear should be lower, giving the storm a better chance of development. None of the reliable forecast models predict that 95L will develop. In their 8 am EDT July 7 Tropical Weather Outlook, NHC gave the disturbance a 40% chance of developing into a tropical depression or tropical storm by Tuesday. I put these odds higher, at 70%. Climatology argues against 95L becoming a tropical depression east of the Lesser Antilles Islands; there have been only 20 July tropical depressions that have formed east of the Lesser Antilles since 1851, an average of one tropical cyclone every eight years.


Figure 3. MODIS image of Hurricane Erick (right) and Tropical Depression Dalila (left) taken at approximately 5 pm EDT Saturday, July 6, 2013. At the time, Erick was a Category 1 hurricane with 80 mph winds. Image credit: NASA.

Hurricane Erick brushes Mexico
In the Eastern Pacific, Tropical Storm Erick weakened from a 80 mph Category 1 hurricane on Saturday to a 70 mph tropical storm on Sunday. Erick is moving away from the southwestern coast of Mexico, and is expected to brush Baja on Monday and bring 2 - 4" of rain as the storm weakens and heads out to sea. The 11 am EDT Sunday wind probability forecast from NHC gave Cabo San Lucas on the tip of Baja a 41% chance of experiencing tropical storm-force winds on Sunday night or Monday.

Jeff Masters

Hurricane

A Gulf of Mexico and an Eastern Atlantic Disturbance Worth Watching

By: JeffMasters, 1:53 PM GMT on July 06, 2013

A tropical disturbance (designated 94L by NHC on Friday) is over the Western Gulf of Mexico, and is headed north towards the Texas/Louisiana coast at 5 - 10 mph. Satellite loops show a modest area of disorganized heavy thunderstorm activity that has been steadily growing this morning. Wind shear has fallen to the moderate range, 10 - 20 knots, since Friday, and the lower wind shear is likely responsible for the increase in thunderstorm activity. A trough of low pressure over the Western Gulf of Mexico is pumping dry air into the west side of 94L, interfering with development. The disturbance should move inland by Sunday morning, bringing heavy rains of 1 - 3" along the Upper Texas and Western Louisiana coasts through Monday morning. None of the reliable forecast models predict that the disturbance will develop, and the disturbance has only a day over water with marginal conditions for development. In their 8 am EDT July 6 Tropical Weather Outlook, NHC gave the disturbance a 20% chance of developing into a tropical depression or tropical storm by Monday.


Figure 1. The Saturday morning NHC Tropical Weather Outlook shows two "Invests" worth watching: 94L over the Gulf of Mexico (area 1), and 95L over the Eastern Atlantic (area 2.) Both were given 20% chances of developing by Monday. Image credit: NHC.

Cape Verdes tropical wave 95L
As we approach mid-July, it's time to begin turning our attention to tropical waves coming off the coast of Africa. We have our first such system worthy of attention today, a tropical wave designated 95L over the Eastern Atlantic near 8°N 33°W, about 800 miles southwest of the Cape Verde Islands. Satellite loops show a modest area of heavy thunderstorms that is showing a moderate amount of spin. Wind shear is moderate, 10 - 20 knots, and ocean temperatures are warm, 28°C. The 8 am EDT Saturday forecast from the SHIPS model predicted that 95L would encounter cooler waters of 27.5°C over the weekend as it headed west to west-northwest at 15 - 20 mph. Wind shear is expected to remain moderate though Monday, which may allow for some additional organization. However, 95L is embedded in a very large area of dry air associated with the Saharan Air Layer (SAL), and July African waves typically have considerable trouble getting organized in the very dry air of the SAL. The disturbance could arrive in the Lesser Antilles Islands as early as Tuesday. A band a strong upper-level winds associated with the subtropical jet stream is expected to be over the northern islands at that time, and if 95L has penetrated as far north as 15°N latitude by that time, it will have to face very high wind shear of 30+ knots. But if 95L stays farther to the south, wind shear should be lower, giving the storm a better chance of development. None of the reliable forecast models predict that 95L will develop. In their 8 am EDT July 6 Tropical Weather Outlook, NHC gave the disturbance a 20% chance of developing into a tropical depression or tropical storm by Monday.


Figure 2. MODIS image of 95L taken at approximately 11 am EDT Saturday, July 6, 2013. Image credit: NASA.

Elsewhere in the tropics
A large upper-level cold-cored low pressure system a few hundred miles north of Puerto Rico will move west over the next dew days, arriving in the Bahamas by Sunday and South Florida by Tuesday. The models do not show that this low will will acquire a surface circulation, and there is only minimal heavy thunderstorm activity associated with it.

In the Eastern Pacific, Tropical Storm Erick is brushing the southwestern coast of Mexico, and is expected to intensify into a Category 1 hurricane on Saturday afternoon. Erick will bring heavy rains of 3 - 5 inches to Southwest Mexico, but the core of the storm is currently expected to remain just offshore. Erick will likely weaken to a tropical storm on Monday, when it will pass just south of Baja.

Cool San Francisco time-lapse fog video
Videographer Simon Christen has created a spectacular 4-minute time-lapse video of fog rushing in past the Golden Gate Bridge into San Francisco. He writes: ""Adrift" is a love letter to the fog of the San Francisco Bay Area. I chased it for over two years to capture the magical interaction between the soft mist, the ridges of the California coast and the iconic Golden Gate Bridge. This is where “Adrift” was born. The weather conditions have to be just right for the fog to glide over the hills and under the bridge. I developed a system for trying to guess when to make the drive out to shoot, which involved checking the weather forecast, satellite images and webcams multiple times a day. For about 2 years, if the weather looked promising, I would set my alarm to 5am, recheck the webcams, and then set off on the 45-minute drive to the Marin Headlands. I spent many mornings hiking in the dark to only find that the fog was too high, too low, or already gone by the time I got there. Luckily, once in a while the conditions would be perfect and I was able to capture something really special. Adrift is a collection of my favorite shots from these excursions into the ridges of the Marin Headlands."


Video 1. Adrift from Simon Christen on Vimeo.

Jeff Masters

Hurricane

Gulf of Mexico Tropical Disturbance Headed Towards Texas

By: JeffMasters, 1:17 PM GMT on July 05, 2013

A tropical disturbance over the Central Gulf of Mexico is headed northwest towards Texas at 5 - 10 mph. Satellite loops show a modest area of disorganized heavy thunderstorm activity associated with the disturbance, which is suffering from high wind shear of 20 - 30 knots due to strong upper-level winds from a trough of low pressure over the Western Gulf of Mexico. Dry air from the trough is also interfering with development. The upper-level trough is expected to weaken and pull to the north over the weekend, potentially bringing slightly more favorable conditions for development over the Gulf of Mexico on Saturday and Sunday. The atmosphere will moisten and wind shear may fall to the moderate range, 10 - 20 knots. The disturbance should move northwest, arriving at the Upper Texas coast by Sunday morning. Heavy rains of 1 - 3" can be expected along the Upper Texas and Western Louisiana coasts Sunday morning through Monday morning. None of the reliable forecast models predict that the disturbance will develop. In their 8 am EDT July 5 outlook, NHC gave the disturbance a 10% chance of developing into a tropical depression or tropical storm by Sunday.


Figure 1. Morning satellite image of the tropical disturbance over the Gulf of Mexico. Image credit: NOAA.

Elsewhere in the tropics
A large upper-level cold-cored low pressure system a few hundred miles northeast of Puerto Rico will move west over the next dew days, arriving in the Bahamas by Sunday and South Florida by Tuesday. Although the models do not show that this low will will acquire a surface circulation and develop tropical characteristics, it will be worth watching for development.

In the Eastern Pacific, Tropical Storm Erick is brushing the coast of Mexico and intensifying, and is expected to bring heavy rains of 3 - 5 inches to Acapulco. The core of the storm is currently expected to remain offshore. Erick's formation on July 4 comes eighteen days earlier than the usual formation date of the season's fifth storm in the Eastern Pacific, July 22.

Jeff Masters

Hurricane

Extreme Jet Stream Bringing U.S. Record Heat, Record Cold, and Flash Flooding

By: JeffMasters, 4:11 PM GMT on July 03, 2013

The jet steam is exhibiting unusual behavior over the U.S., a pattern we've seen become increasingly common in summertime over the past decade. There's a sharp trough of low pressure over the Central U.S., and equally sharp ridges of high pressure over the Western U.S. and East Coast. Since the jet acts as the boundary between cool, Canadian air to the north and warm, subtropical air to the south, this means that hot extremes are penetrating unusually far to the north under the ridges of high pressure, and cold extremes are extending unusually far to the south under the trough of low pressure. The ridge over the Western U.S., though slowly weakening, is still exceptionally intense. This ridge, which on Sunday brought Earth its highest temperatures in a century (129°F or 54°C in Death Valley, California), was responsible for more record-breaking heat on Tuesday. July 2. Most notably, Redding, California hit 116°, just 2° short of their all-time record. Death Valley had a low of 104°, the second hottest night on record since 1920 (the hottest was just last summer!) Numerous daily high temperature records were set in Arizona, California, Nevada, Utah, Montana, Oregon, and Washington. It was the opposite story in the Central U.S., where the southwards-plunging jet stream allowed record cold air to invade Texas. Waco, Texas, hit 58°F this morning (July 3), the coldest temperature ever measured in July in the city. Numerous airports in Texas, Nebraska, Arkansas, Louisiana, Kansas, and Missouri set new daily record low temperatures this morning. And over the Eastern U.S., the northward-pointing branch of the jet stream is creating a potentially dangerous flooding situation, by pulling a moisture-laden flow of tropical air from the Gulf of Mexico over the Florida Panhandle north-northeastward into the Appalachians. Up to five inches of rain is expected over this region over the next few days, and wunderground's severe weather map is showing flash flood warnings for locations in Florida, Georgia, South Carolina, and North Carolina.


Figure 1. Jet stream winds in the upper atmosphere at a pressure level of 300 mb on July 3, 2013. The jet had an unusually extreme configuration for summer, with a sharp trough of low pressure over the Central U.S., and equally sharp ridges of high pressure over the Western U.S. and East Coast. Image from the wunderground jet stream page.


Figure 2. Predicted precipitation for the 7-day period ending Wednesday, July 10, 2013. Image credit: NOAA/HPC.

Third extreme jet stream pattern of the past five weeks
This week's extreme jet stream pattern is the third time in the past five weeks that we've seen a highly amplified ridge-trough pattern that has led to extreme weather. The others:

1) The end of May and beginning of June, when the $22 billion Central European floods occurred. A high pressure ridge became stuck over northern Scandanavia, causing all-time May heat records--as high as 87°F--at stations north of the Arctic Circle in Finland. The high pressure ridge blocked low pressure systems from moving north, and a series of two low pressure systems dumped record rains over Austria and Germany, creating the highest floods ever seen on portions of the Danube River. The $22 billion price tag made it the 5th most expensive non-U.S. weather-related disaster in world history.

2) June 18 - 22, when a ridge of high pressure over Alaska broke all-time heat records in the state, with unofficial readings as high as 98°F. A low pressure system became trapped over Alberta, Canada, bringing the city of Calgary a $3 billion flood disaster. This was the most expensive flood in Canadian history, and third most expensive natural disaster of any kind for the country. The only more expensive disasters were a 1989 wildfire ($4.2 billion) and a 1977 drought ($3 billion.)

As I discussed in a March 2013 post, "Are atmospheric flow patterns favorable for summer extreme weather increasing?", research published this year by scientists at the Potsdam Institute for Climate Impact Research (PIK) in German found that extreme summertime jet stream patterns had become twice as common during 2001 - 2012 compared to the previous 22 years. One of these extreme patterns occurred in August 2002, during Central Europe's previous 1-in-100 to 1-in-500 year flood. When the jet stream goes into one of these extreme configurations, it freezes in its tracks for weeks, resulting in an extended period of extreme heat or flooding, depending upon where the high-amplitude part of the jet stream lies. The scientists found that because human-caused global warming is causing the Arctic to heat up more than twice as rapidly as the rest of the planet, a unique resonance pattern capable of causing this behavior was resulting. According to an email I received from German climate scientist Stefan Rahmstorf, one of the co-authors of the study, unusually extreme jet stream amplitudes likely played a role in the May - June Central European flooding event.

Tropical disturbance in the Gulf of Mexico
Yellow means caution: the National Hurricane Center (NHC) has drawn a yellow circle on their Graphical Tropical Weather Outlook around an area of disturbed weather in the Gulf of Mexico. In their 8 am EDT July 2 outlook, NHC gave the region a 10% chance of developing into a tropical depression or tropical storm by Friday. Satellite loops show only minimal heavy thunderstorm activity associated with the disturbance, which is suffering from high wind shear of 20 - 30 knots. Dry air due to the presence of an upper-level trough of low pressure over the Western Gulf of Mexico is also interfering with development. The upper-level trough is expected to weaken and pull to the north late this week, bringing more favorable conditions for development over the Southern Gulf of Mexico's Bay of Campeche by Friday. The atmosphere will moisten and wind shear may fall to the moderate range, 10 - 20 knots. The disturbance should move west to west-northwest, arriving near the Texas/Mexico border region on Monday or Tuesday. None of the reliable forecast models predict the disturbance will develop.

Elsewhere in the Atlantic
A large upper-level cold-cored low pressure system over the middle of the North Atlantic will move to the southwest during the week, and this low is expected to arrive in the Bahamas by Sunday and South Florida by Monday. Although the models do not show that this low will will acquire a surface circulation and develop tropical characteristics, it will be worth watching for development late this week.

Jeff Masters

Extreme Weather Heat Flood

Historic Heat Wave Reponsible for Death Valley's 129°F Gradually Weakening

By: JeffMasters, 4:22 PM GMT on July 02, 2013

One of the greatest heat waves in North American history peaked on Sunday and Monday, but will still bring some of the hottest temperatures ever recorded to portions of the Western U.S. during the afternoon today. The extraordinary heat wave, caused by an unusually extreme standing wave pattern in the jet stream, brought Earth's highest June temperature ever recorded on Sunday, June 30, when the mercury hit 129.2°F (54.0°C) in Death Valley, California. The only higher temperatures ever recorded on the planet occurred in Death Valley on July 10, 12, and 13, 1913, when readings of 134°F, 130°F, and 131°F were recorded. This 100 year-old record heat wave has many doubters, though, including Mr. Burt, who noted in a 2010 blog post that "The record has been scrutinized perhaps more than any other in the United States. I don't have much more to add to the debate aside from my belief it is most likely not a valid reading when one looks at all the evidence. Normally when Death Valley records its hottest temperatures they occur during region-wide heat waves. On July 10, 1913 the next highest temperatures recorded in southern California (aside from Greenland Ranch) were just 119° at Heber and 118° at Mammoth Tank." If Mr. Burt is correct, then this Sunday's temperature of 129.2°F in Death Valley was the hottest temperature in recorded history on Earth.


Figure 1. The official Furnace Creek, Death Valley maximum recording thermometer for the maximum temperature measured on June 30th, 2013. The 129.2°F reading was the highest June temperature ever measured on Earth. Photo courtesy of Death Valley National Park and NWS-Las Vegas.

As documented by Mr. Burt in this latest blog post, some of the all-time records from the 2013 heat wave:

June 27, 2013
102° Santa Fe, NM: all-time heat record
105° Albuquerque, NM: tied 2nd highest temperature on record

June 28, 2013
105° Salt Lake City, UT: hottest June temperature on record
114° Zion National Park, UT: hottest June temp on record, and only 1° short of their all-time record of 115°

June 29, 2013
100° Ely, Nevada: hottest June temperature on record (previous 99° June 22, 1954)
101° Eureka, Nevada: hottest June temperature on record (previous 98° on two occasions)
105° Salt Lake City, Utah: hottest June temperature on record (again, see June 28)
122° Palm Springs, California: hottest June temperature on record (tied June 28, 1994) and 1° short of all-time record of 123° set on August 1, 1993
128° Death Valley, California: hottest June temperature on record (tied previous 128° set on June 29, 1994)
It was 119° in Phoenix, Arizona their 4th warmest reading on record.

June 30, 2013
129° Death Valley, California: Earth's all-time hottest June temperature
115° Lancaster, California: all--time heat record (previous record 114° on July 18 and 19, 1960)
117° Las Vegas, Nevada: all-time heat record (tied with July 19, 2005 and July 24, 1942)

All-time June monthly records were set or tied at:
104° Elko, Nevada (previous 104° June 24, 1981)
103° Tonopah, Nevada (previous 102° on two occasions), this was also just 1° short of their all-time record of 104° set on July 18, 1960).
106° Winnemucca, Nevada (previous 106° on June 24, 1988)

July 1, 2013
127° Death Valley, California
110° Boise, Idaho: tied for 2nd hottest temperature on record

Deadly Yarnell, Arizona fire continues to burn out-of-control
The deadly Yarnell Hills, Arizona wildfire that claimed the lives of nineteen firefighters of the Prescott-based Granite Mountain Hotshots continues to burn out of control near Yarnell, a small town about 85 miles northwest of Phoenix. The fire has burned 8,400 acres (13 square miles) and was 0% contained on Tuesday morning. Temperatures in the upper 90s are expected Tuesday afternoon near Yarnell. These temperatures are about five degrees cooler than during Sunday's deadly blaze. The intense ridge of high pressure responsible for the intense heat will continue to weaken during the week, and high temperatures will be in the low 90s by the end of the week.


Figure 2. The Yarnell Hill Fire burns through the town of Yarnell, Ariz. on Sunday, June 30, 2013. The fire started Friday from a lightning strike and killed nineteen firefighters on Sunday. (AP Photo/The Arizona Republic, Tom Story)

Radar imagery from Sunday showed numerous dry thunderstorms over the Yarnell area, and it is likely that the outflow from one of these thunderstorms caused a sharp wind shift and strong wind gusts that caused extreme fire behavior that overran the firefighters' escape route. According to The Arizona Republic, the firefighters were trapped between two ridges when the winds suddenly reversed. A fire-monitoring station four miles from the fire measured nearly record combustion levels for the fuel on the ground, in the 97th percentile since the station was installed in 1985. The station measured southwest winds gusting to 15 to 25 mph at 4:01 PM. One hour later, ten minutes after the firefighters had deployed their fire shelters, the wind had reversed direction to northeast, and was gusting at 30 to 47 mph. The topography could have channeled these wind gusts to even higher speeds where the firefighters were. "Guys on the ground told me the fire behavior was as extreme as anything they’d ever seen,” said Dugger Hughes of the Southwest Coordination Center, an interagency organization in New Mexico that coordinates state and federal firefighting resources. The flames were 40 feet high and moved at an average speed of 1/2 mph. According to WWF blogger Nick Sundt, who is a former "smokejumper", dry thunderstorms causing sudden wind gusts and wind shifts is a common scenario with such large scale firefighter fatality incidents: for example, in the 1949 Mann Gulch fire in Montana (thirteen firefighters killed), and in the 1994 Storm King Mountain or South Canyon Fire in Colorado (fourteen firefighters killed.) Nick commented in an email to me: "It happened once to me in Idaho late one afternoon (in 1981, I think) when gusts from a building thunderstorm caused a fire to blow up in a drainage I was in with other smokejumpers.  We popped our fire shelters but the winds shifted late in the night and the fire stopped short of us. We high-tailed it out of there early in the morning before the winds picked up and incinerated everything we left behind (parachutes, jump gear, etc)." Wunderblogger Lee Grenci analyzes the 3-dimensional characteristics of the atmosphere over Arizona over the weekend in his latest post. He shows how conditions were ideal on Sunday for spawning dry thunderstorms capable of bringing erratic, gusty winds to the fire region. Here is the "Spot Forecast" that the Granite Mountain Hotshots had to work with on Sunday:

FNUS75 KFGZ 301655
FWSFGZ

SPOT FORECAST FOR YARNELL HILL...ARIZONA STATE FORESTRY
NATIONAL WEATHER SERVICE FLAGSTAFF AZ
945 AM MST SUN JUN 30 2013

FORECAST IS BASED ON REQUEST TIME OF 0939 MST ON JUNE 30.
IF CONDITIONS BECOME UNREPRESENTATIVE, CONTACT THE NATIONAL WEATHER SERVICE.

DISCUSSION...STRONG HIGH PRESSURE OVER THE SOUTHWEST WILL MAINTAIN THE HEAT SPELL FOR THE NEXT SEVERAL DAYS. LIMITED MOISTURE WILL RESULT IN ISOLATED THUNDERSTORM ACTIVITY TODAY AND MONDAY. THESE STORMS WILL PRODUCE LIGHTNING AND STRONG AND GUSTY WINDS...BUT LITTLE OR NO MEASURABLE PRECIPITATION. TEMPERATURES WILL DECREASE SLIGHTLY AND MINIMUM RELATIVE HUMIDITY WILL SLOWLY INCREASE OVER THE NEXT FEW DAYS.

TODAY...

SKY/WEATHER.........PARTLY CLOUDY. A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS IN THE AFTERNOON.
MAX TEMPERATURE.....100 TO 103.
MIN HUMIDITY........11 TO 15 PCT.
WINDS (20 FT).......EAST WINDS AROUND 5 MPH...BECOMING SOUTHWEST
WITH GUSTS UP TO 20 MPH IN THE AFTERNOON.
LAL.................2.
HAINES INDEX........5 MODERATE.

TONIGHT...

SKY/WEATHER.........PARTLY CLOUDY. A SLIGHT CHANCE OF SHOWERS AND
THUNDERSTORMS IN THE EVENING.
MIN TEMPERATURE.....73 TO 76.
MAX HUMIDITY........35 TO 40 PCT.
WINDS (20 FT).......WEST WINDS AROUND 10 MPH. GUSTS UP TO 20 MPH
EARLY IN THE EVENING.
LAL.................2.
HAINES INDEX........5 MODERATE.

MONDAY...

SKY/WEATHER.........PARTLY CLOUDY. A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS IN THE AFTERNOON.
MAX TEMPERATURE.....98 TO 102.
MIN HUMIDITY........13 TO 17 PCT.
WINDS (20 FT).......SOUTH WINDS AROUND 5 MPH...BECOMING SOUTHWEST WITH GUSTS UP TO 20 MPH IN THE AFTERNOON.
LAL.................2.
HAINES INDEX........5 MODERATE.

$$
FORECASTER...DB
REQUESTED BY...BYRON R KMIBALL
REASON FOR REQUEST...WILDFIRE
TAG 20130630.YARNE.01/FGZ

The shocking and sad deaths of the nineteen brave men who died on Sunday was the largest loss of life among wildfire firefighters since 1933 Griffith Park, California fire in the U.S. (25 killed.) Fighting wildfires is dangerous work, and 1,043 firefighters died between 1910 - 2012 fighting wildfires in the U.S., according to statistics from the National Interagency Fire Center. Firefighter deaths have been on the rise in recent decades. Over the past ten years, 2004 - 2013, there have been an average of sixteen of these deaths per year, compared to eleven deaths per year during the 1970s and 1980s.

Links
Experts See New Normal as a Hotter, Drier West Faces More Huge Fires New York Times, July 1, 2013
The Climate Context Behind the Deadly Arizona Wildfires Climate Central, July 1, 2013

The tropical Atlantic is quiet
There are no threat areas in the Atlantic to discuss today, and none of the reliable forecast models predict tropical cyclone development through Sunday. There is a large upper-level cold-cored low pressure system over the middle of the North Atlantic that will move to the southwest during the week, and this low is expected to arrive in the Bahamas by Sunday and bring rainy conditions. Although the models do not show that this low will will acquire a surface circulation and develop tropical characteristics, it may be worth watching for development late this week.

Jeff Masters

Heat Fire


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Category 6™

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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather