THURSDAY EVENING UPDATE ON MEMORIAL DAY WEEKEND FORECAST & 90L
STARDATE 201805.24 12315 HRS
The good news is that as we move into the Memorial Day weekend ... the various weather models are in better agreement with regard to how much rain is going to fall .. where .. and when .. across the Middle Atlantic region on Friday Saturday Sunday and Monday..
Part of the reason why the models are in better agreement is that they are "detecting" or " seeing" the tropical system -- HERE AFTER KNOWNS AS 90L - coming out of the Northwest Caribbean with much more detail and precision. This makes for more reliable forecasts.
Part of the problem earlier was that the GFS model was moving the system much faster while and the European model showed a much slower track north . With a much faster movement north ... 90L would be able to get further inland quicker and therefore its associated rains could get into the Middle Atlantic region faster and have a bigger impact. The European model over the past few days has consistently showed a slower 90L... which means its rain shield will take longer to get this far north AND the rain shield will come in weaker and does not get nearly as far north with the same sort of impact.
This image shows current Thursday afternoon satellite picture of the tropical system. I have highlighted the feature in yellow. It certainly is impressive cloud mass and the potential for the system to develop this weekend into a tropical depression or possibly a tropical storm is pretty high.
These images from the NHC show the details of the discussion. They give the system an 80% chance of development over the next several days and I see no reason to go against that assessment. Many of the globals model do show 90L just reaching Minimal Hurricane threshold as it nears LA MS/ AL coast on Monday.
These next few images show the development of the system over the next several days. These maps are from the European model. Notice that the system takes a turn to the northwest as it moves into the eastern Gulf of Mexico. This is because of a large ridge in the jet stream which at the surface is producing HIGH pressure area off the Southeast U.S. Coast. This HIGH pressure area is often refer to as Bermuda High. The tropical system is going to have to go around the northwest side of this HIGH pressure ridge and that is why 90L will turn towards NW during the weekend... and NOT come up the southeast US coast. Because the overall system is slower the rains take longer to get here and have a better chance of weakening as the systems comes North.
This images from the Thursday afternoon GFS (left) and European ( right) models valid for Friday --the total rainfall by 11:00 PM Friday night. The GFS has scattered light to moderate rain over portions of southwest North Carolina ... in far southwest Virginia ...while the European model is much lighter with his precipitation. Both models do not have the precipitation moving into these areas until Friday evening. We think the European solution here is correct. The European solution is supported by the high resolution Canadian which keeps most areas drive through Friday afternoon evening even over Western North Carolina.
For Saturday even though there are Lots of colors and it looks ominous on these maps ...with respect to rainfall these maps are little deceiving. For example the dark green colors only represent a 0.20" of an inch of rain which is not much. Again the GFS model is substantially heavier with rainfall amounts especially over all of southwest Virginia ...and along the Virginia North Carolina border ...into the Peninsula and central Chesapeake Bay areas. In that region the GFS model has 0.5-1.0"/12-38mm rains TOTAL for the day on Saturday. The European model substantially drier and keeps all of eastern and southeastern Virginia dry without any significant rain especially in Southeast Virginia and the Chesapeake Bay. Even the rains over the Shenandoah Valley and the northern Virginia Piedmont are significantly lighter on the European than they are in the GFS.
The one area the models do agree upon is over Northwest North Carolina and West Virginia seeing more organized steady rain. Again and the situation we favor the European model over the GFS.
In other words for Southeast Virginia ...we believe that most of Saturday will be rain free and this also be the case for eastern North Carolina and the Chesapeake Bay. Any light to moderate rain will be out to the west of I-95 and across the Virginia Piedmont as well as western half of North Carolina. Even in these rainy areas.. most of the day will be rain free with scattered showers and not steady all the rain. And the data shows none of this activity will be thunderstorms
The model agreement is a little better on Sunday with light to moderate rain even showing up over most of Virginia on the European model. Only over Hampton roads and the eastern third of North Carolina ... does it stay relatively dry on Sunday. The rest of Virginia Maryland and the Delmarva see light to moderate rates with most of the rainfall amounts ranging between 0.1-0.5 inches with a few isolated higher amounts over southwest Virginia and the Northern Virginia Piedmont.
The GFS model similar and fact is a little drier over eastern Virginia then the European model.
Finally taking a look at Monday we see significant rain coming up from the Deep South on both of the models but the issue is timing. The European model has heavy rain over far southeastern North Carolina whereas the GFS has that rain across the entire state and North Carolina pushing into Hampton roads. The GFS even has a bull's eye or cluster of 2 -4" rains in Northeast North Carolina up to the Virginia North Carolina border. Both models to agree that central and northern Virginia as well as the southwest Virginia should not see significant rain on Monday. There may not be a lot of sunshine but most areas you should stay dry. However North Carolina has a real good chance of seeing moderate rain developing by midday and continuing into the evening hours on Monday May 28th.
90L COMING TO NC/ VA? ... SEEMS SO
90L/ tropical system will probably reach high end tropical storm intensity this weekend. In fact there is a small chance that it could even reach minimal category 1 hurricane status before it makes landfall on the Mississippi Alabama or Southeast Louisiana Coast on Tuesday, May 29. Most of the weather models are turning 90L once it comes inland ...to the North and then NE as it moves into Virginia and/ or North Carolina MAY 30 - JUNE 1 weekend as we go into the first weekend of JUNE. This sort of track is bad news for those looking for dry conditions in North Carolina Virginia and Maryland next weekend. Of course we don't know how much rain 90L is going to have by the time it gets this far north and or/how organized this tropical system's remains will be when it begins to drift to the northeast.
The weather models show that strong Bermuda HIGH still off the Southeast US Coast and a huge ridge or dome developing in the jet stream over Texas and Northern Mexico. These two features will create a pathway so this tropical system will turn to the northeast at some point next week and move into the Middle Atlantic region.
It will be greatly weakened and it will not have high winds with it. Instead we are looking..worst case ..an organize area of the moderate rainfall.
In addition because of the jet stream pattern ...a new piece of energy coming down from the Great lakes will reinforce this feature and establish a trough over the East Coast June 1 and 2 which could prolong the rain especially on the coastal areas right through to a June 4. Again it is too early to know if we're talking about steady rain or just scattered showers were something in between. But as it stands right now the first weekend of June does not look to be ideal.