Vacation

I will be entertaining guests for the next 5 days, so I will not be making any updates until Saturday. Try to enjoy the active tropics and lets hope the storms turn out to sea. Sadly, I think 92L has a very good chance of making landfall at least somewhere in the Caribbean...if not Florida and then into the Gulf. Currently the models have a very good consensus on a northwest movement north of the windwards and Puerto Rico into the Bahamas. After that the models diverge with tracks going into the Gulf and up the eastern seaboard. We will have to wait and see.

Hurricane Hernan and Lesson in Model Variation

Hurricane Hernan

I have a great image of Hurricane Hernan which I thought I would share. The system is currently in the eastern Pacific moving into cooler waters, thus the reduction in deep convection, but the storm still has great outflow.

Model Variation

If you look down two posts you will see the model output from 12Z yesterday from the European model. A quick glance at the new model from today at 12Z at 216 hours out (to remain consistent) and you will see that the #1 and #2 storms have switched locations. This indicates a change in the mid- to upper-levels which guides the track of tropical systems. If only one of these first two systems develops, the flip-flop in the track could be a major issue in the long term.

Yesterday's Weather

NWS Forecast High: 88F
My Forecast High: 88F
Actual High: 90F!

Wait, so how did it get to 90F yesterday?! Well, I am still not fully sure. Skies stayed clear, but 850 mb temps were a bit cooler. Again, the temp peaked at 90F for our hour and immediately dropped back down after the clouds moved in. I guess one extra hour of heating was too much and the temperate peaked a bit warmer than expected. However, once again, Philip was the warmest location in the region.

Rainfall: 0.03 inches....but again, I am not sure how it was only that much. A very potent line of storms developed over the Black Hills and to the north and south. This line moved east through the evening, slowly weakening, but still with rainfall rates of at least 0.10-0.25 inches an hour. Some how this line was only able to produce rainfall of 0.03 inches in Philip when it recorded precipitation for three hours! Either way, my forecast was very close to correct for yesterday. Yesterday was definitely the best chance of rainfall over the past weekend as I predicted.

Today so far: Today has been much cooler than yesterday, as I expected. I almost added text saying that it could be even cooler than 86F and it looked like it might after sitting at 81F for two hours. However, now Philip is up to 85F which should be about as warm as it gets considering thunderstorms have developed over the Black Hills bringing cloud cover over the plains. The forecast of rainfall in the morning did not pan out as the cold front moved through the area, but there is still a chance of rainfall through the afternoon hours if any storms roll off of the Hills. They have been having trouble today, likely because the main forcing has already pushed to the east, thus decaying the storms when they move away from the higher elevations.

European Model

When was the last time I saw THREE tropical systems on the European model in the Tropical Atlantic at the same time? NEVER! Yes, things are definitely going to start getting active. The storm along the southeast coast is the current 92L, or the most impressive system currently out in the Atlantic (the western system in the TWO described in the Tropical Update earlier today), #2 in the Caribbean is the system the GFS has been developing for a while now (TWO eastern system), and system #3 is the wave currently coming off of the African coast. Should get very active soon in the Atlantic.

12Z European Model at 240 hours

Philip, SD Weather Update

Yesterdays Forecast Specifics:

NWS Forecast: 91F
My Forecast: 88F
Actual High: 91F

What happened? Philip was the only city in the area to reach a high in the 90s. In fact, Pine Ridge, a location that is often warmer than Philip, only reached 89F. The reason was that cloudy conditions did not move in quite as quickly as predicted. Once the clouds moved in, the temperature dropped from 91F to 88F in an hour. My forecast wasn't bad...just unlucky.

NWS Forecast low: 64F
My Low: 65F
Actual Low: 63F

What happened? Nothing too substantial here. Dewpoints went a degree lower than I thought and the temperature approached it much more efficiently.

Rainfall: None

What happened? Storms developed in the Black Hills as I expected, but a widespread heavy rain or thunderstorm event was just not in the cards. Some thunderstorms developed as an upper level system traversed through the area, but the most robust lift and forcing was either too far south (NE/KS/OK) and further west (ID/MT/WY) which was what I expected.

Conditions expected today:

I still like my forecast of 88F (NWS: 88F). There should be much more cloudiness than yesterday and considering Philip was able to reach 91F yesterday, I think it will be just a few degrees cooler with winds out of the southeast at 5-15 mph today. Thunderstorms look to develop in the mid afternoon as CAPE values approach 1500 J/kg and CIN degrades. LI will have values near -5, helicity will be minimal (< 100), and preciptable water will be near 1.5 inches. With low helicity, the threat of tornadic storms looks to be minimal. However, with steep lapse rates and decent instability there should be a few severe thunderstorms today, with hail being the primary threat. A strengthening low level jet in the evening will lead to a greater wind threat, but the low level jet doesn't look to be too substantial this evening as compared to past events. I think we will see some heavy rainfall and large hail in the Black Hills followed by storms moving east through the late afternoon into the evening as a cold front and upper level disturbances move through the region.

Tomorrow morning also looks to be an active time period, with decent instability once again present over the area as the cold front continues to traverse South Dakota and North Dakota. Severe weather is once again possible. Highs could be substantially cooler than on Sunday with 850 mb temps forecasted to be near 17C by the NAM in the peak heating period in the afternoon. However, the GFS brings 850 mb temps back up to 20C by 7pm. This would give a range of 77F-86F. MOS has a large range as well with GFS at 94F and ETA at 86F. Considering the GFS MOS has no rainfall, and rainfall looks likely in my opinion today through mid-afternoon tomorrow, I am going to lean closer to the cooler solution. 86F sounds good at this time. (NWS: 87F).

Tropical Update August 10th, 2008

I made one major mistake yesterday in my blog post, and that was that the GFS was a little fast in forecasting a system to develop in the mid-Atlantic in 3-5 days. After looking at another day's worth of model runs, consistency from other models (including the UKmet, European, and CMC) and it looks much more likely that a system will develop in the mid-Atlantic in the next 3-5 days. I don't think the question is will a storm develop, but rather how strong it will be and where it will go.

There are three possible locations in which a tropical system could develop in the next week. Two disturbed areas are currently located in the central Atlantic, highlighted on the Tropical Weather Outlook below. Both systems are categorized in the moderate risk of development category by the National Hurricane Center with text saying "some development is possible during the next couple of days." In other words, the NHC is interested in these locations for possible development.

In the satellite picture below I have circled the two disturbed locations. Both seem to have some cyclonic turning and are located in regions of low shear, high sea surface temperatures, and have some decent convection. The system to the west currently looks the most robust, but the models are having trouble developing that system (except for the CMC) and instead develop the eastern system. If I had to pick one to develop in the next two days, I would pick the system to the west with its strong convection and greater separation from the ITCZ. The main inhibiting factor is the very dry air to the west of the system which could cut off its development quickly. The eastern system still has to break away from the ITCZ to get itself together. However, I do expect it to develop in 3-5 days just as all of the models are predicting in a favorable environment.

The models vary strongly on the strength and track of the system. The GFS and CMC develop the eastern system quickly, in 2-4 days, and strengthen it to a hurricane, maybe even a major, before it reaches the islands. If this is true, the storm will be strong enough to feel the trough along the eastern seaboard and pull north as a developing low pressure system emerges off of the Carolinas. However, the European does not develop the system quite as quickly, and keeps the system weak. This allows it to slide under the trough and into the Gulf of Mexico.

Further systems are forecasted to develop behind these two current waves, including one wave that is moving off of the African coast as we speak. All three models (GFS, CMC, and European) develop this wave and move it across the Atlantic towards land. Obviously we are entering a busy period in the tropics! Below are the GFS and European model solutions for the eastern system shown in the satellite picture above. This system is numbered #1, followed by the African coast system as #2, and then further into the future systems as higher numbers. The model output is from hour number 240, or 10 days out.

GFS:

European:

So what does this tell us? We need to keep watching these systems as all of the models forecast them to impact land at some point. The GFS solution seems like the worst case scenario with a strong system moving up the eastern seaboard, possibly impacting New York. However, at 10 days out this is very difficult to forecast. Remembering back to the discussion of Asia yesterday, our only hope is that the eastern trough doesn't break down as fast as the models are predicting and the system numbered #1 is brought out to sea. However, considering the models keep forming systems in the Atlantic, I think it is safe to say the United States is definitely at risk for further landfalls this season.

Tropical Update August 9th, 2008

Asia:

Just a few comments on the tropics in Asia. Currently there is a large trough just off the east coast of Japan, and the trough looks to continue for the next week in this region per the European model. This would hint at troughiness continuing along the eastern seaboard of the United States as well for the next 14-20 days! Conditions in Japan often coincide with conditions on the eastern seaboard of the United States in 7-10 day delay. Thus, the model forecasts of the trough starting to break down in the eastern United States might be a bit too bullish, and the troughiness might continue for some time. Which, in the long run, could be a good thing considering the more active hurricane period coming up.

Another note: No tropical systems are forecasted by the European model in Asia over the next 10 days at this time. This is good news for the Olympic games. Beijing isn't often directly impacted by a tropical system landfall considering they are so far north and a bit inland, but any remnants could impact the games with heavy rainfall. So, for right now, conditions look good for the coming up week to ten day period.

Tropical Atlantic:

Conditions are starting to look conducive for tropical development in the next 3-5 days through the end of the month. A conducive MJO is currently traversing across the central and eastern Pacific Ocean, and will move into the Atlantic in 7-10 days. This should lead to enhanced lift in the tropics, which will lead to more impressive tropical waves and more tropical development. El Nino is forecasted to stay neutral through the rest of the hurricane season.

Shear is currently low in the central Atlantic (5-20 knots), but is still high in the Caribbean Sea (30-50 knots). The GFS forecast over the next week forecasts shear to reduce in the Caribbean Sea, but the CMC does not. Strong shear looks to enhance just north of the preferred tropical wave trajectory path across the central Atlantic, but this shouldn't be a great hindrance to tropical development. If systems do move into this region, they wouldn't be a threat to the land anyway because they would be too far north to traverse across the entire Atlantic before moving north and out to sea.

Sea Surface Temperatures look conducive for development from the African coast all the way to the United States as long as systems stay south of 15N to 45W. Cooler temperatures are currently present in the southern Caribbean as well, but not cool enough to destroy a tropical system. Tropical Cyclone Heat Potential is most conducive for rapid intensification in the northwest Caribbean, the Bahamas, southeast Gulf of Mexico and in the extreme southern Atlantic near 10N, 40W.

So what are the models saying? The European, CMC, and GFS are all predicting tropical waves to start pushing off of the African coast in higher numbers in 7-10 days. The GFS predicts a current tropical wave in the central Atlantic to produce a tropical system in 3-5 days, which might be a bit too fast at this time. However, the wave is in a region of low shear, high sea surface temperatures, upper level divergence, has a reasonable cyclonic rotation, and decent convection. However, little lower level convergence is currently present and the system is still embedded in the ITCZ. If it can break away from the ITCZ it could have a chance at development, but the system is not too impressive just yet.

Beyond this system, little is currently active in the tropical Atlantic. The European, GFS, and CMC all predict an area of low pressure to develop in the central United States and move off of the southeast coast in the 3-5 day time frame. If the system is able to sit over the warm tropical waters of the gulf stream for a few days it could transition into a tropical system. But the models want to bring it quickly to the northeast and out to sea, which shouldn't allow it to develop. Further storm systems are predicted in the tropical Atlantic by all three models after 5 days, but none of these waves have moved off of the African coast just yet.