The Eyewall

One-sentence summary

Impacts from Calvin will diminish later today in Hawaii, while in the Atlantic Don swirls and a couple tropical waves will stir.

Happening now: Calvin hitting Hawaii, while Don swirls in the Atlantic

Heavy rain continues to fall across Hawaii as Calvin passes through today. As of 2 AM Hawaii time, over 5 inches has fallen just west of Hilo in the upslope terrain there, while Hilo itself has seen just shy of 2 inches. Continued rain bands are likely over the next 6 to 12 hours before things settle down.

Winds have been mostly gusting into the 30 mph range in spots, with gusts as high as 45-50 mph or so right now at high elevation. Winds should be near their peak now before things slowly improve this morning. The strongest winds over the next few hours will be over and just downwind of terrain across the islands. Overall, things will improve later today from east to west.

Meanwhile on the Atlantic side, Tropical Storm Don continues its maneuvering in the open waters.

We’re starting to see the exit strategy come into view now, with Don expected to continue its loop and turn northwest, north, and eventually accelerate northeast out to sea. Don’s remnants will likely be absorbed into the jet stream and head into Europe next week as part of a storm system there, as is often the case with recurves.

The medium range (days 6 to 10): Atlantic waves march west but have a lot of dry air to fight off

Two days ago, I wouldn’t say I was bullish on the medium range, but I saw a pathway toward a depression or storm. Today? Not so much. I just really think the dust is too extensive out there to allow for anything to get going. That said, the National Hurricane Center did peg a tropical wave in the eastern Atlantic with a 20 percent chance of development over the next 5 to 7 days as it comes west.

You can see from the map above that any waves will have to navigate this drier air to get going. That won’t necessarily be easy. These waves are worth monitoring, but I really do believe they will struggle a bit through days 7 or 8 as the lead wave approaches the islands.

Meanwhile, in that dry air is a lot of Saharan dust, and that will be making its way across the Caribbean and into the Bahamas, Cuba, and Florida over the next couple days. Eventually, that should arrive in the Gulf and impact the U.S. Gulf Coast and parts of Mexico too.

So look for haze, milky or brown colored skies, some airborne irritants, and hopefully some above average sunrises or sunsets in those areas next week.

Fantasyland (beyond day 10): One trick ponies

The GFS operational model is essentially a one trick pony until August. It usually fires up storms, mostly unrealistic ones, and then eventually corrects to reality in time. We may be seeing that now with the tropical wave in the Atlantic that it periodically tries to blow up as it moves toward the US Southeast coast.

There remains very little ensemble support for this type of outcome. Remember, ensembles differ from operational models in that they are run multiple times with tweaks in the initialization that allow for a broader and more realistic array of potential outcomes. That ensemble support has held steady this week, meaning a small minority show it happening, but we have not added any to that. This tells me that there is not much support for this outcome, and as discussed above, I think this dry air is really going to hamper things. So, yes, we’ll keep watch, but right now, we don’t expect a lot to come of things through the end of July.

One-sentence summary

Tropical Storm Calvin will bring impacts to Hawaii later today and tomorrow, while Don stirs in a slowly awakening Atlantic.

Happening now: Hawaii readying for impacts from Tropical Storm Calvin

This is typically going to be an Atlantic-focused tropical blog, but truth be told, when something interesting or notable is happening elsewhere, it behooves us to offer some insights. Enter: Calvin. We discussed Calvin yesterday, and today we will watch for a close pass near the Big Island of Hawaii.

A Tropical Storm Warning was issued yesterday for the Big Island. From the satellite image above, you can see that Calvin is not greatly organized but it clearly has a lot of moisture as indicated by the bright colors on satellite. Right now, maximum winds are 45 mph, making Calvin a minimal tropical storm. But the combination of a weakening tropical storm, high pressure to the north, and some terrain will likely lead to a healthy wind event over many of the Hawaiian Islands, even those not under TS Warnings.

As the storm approaches Hawaii today, we’ll see rain pick up this evening (island time). Rain will be heavy at times on Tuesday night and Wednesday morning before slowly winding down Wednesday afternoon and evening. This will be a quick storm. For most populous locations, it will be a bit breezy with periods of rain. The heaviest rain and strongest winds will impact the Big Island and Maui. Wind gusts on Mauna Loa and Mauna Kea, as well as around Haleakalā on Maui are expected to be 50 to 65 mph, while at Hilo winds should gust to 40 mph. The Kona side of the Big Island will gust to about 30 mph. Elsewhere, we will see winds of wind advisory or high wind warning criteria in Maui County, as well as perhaps even in Oahu.

Rain totals are expected to peak in the 4 to 8 inch range on the windward slopes of the Big Island and the North Shore and eastern portions of Maui, with lesser amounts on the other islands. Hilo will probably see 4 to 6 inches of rain, while the Kona side of the Big Island will see 1 to 2 inches or a bit less. Flooding is likely in spots, particularly on east and southeast facing slopes, and a Flood Watch is posted for Maui, Molokai, Lanai, Kahoolawe, and the Big Island. Conditions will calm some on Thursday and beyond.

Shifting back to the Atlantic, Subtropical Depression Don reformed into a Tropical Storm on Monday evening. It continues to meander in the open waters between Bermuda and the Azores, with maximum winds of 40 mph.

It remains no threat to land.

The medium range (days 6 to 10): Keeping an eye on the Main Development Region

Yesterday, we discussed the potential for a tropical wave emerging off Africa to maybe, possibly develop as it came west over the next week or so. There remains a bit of model support for this outcome, albeit not a ton. One thing that this or any wave right now will have to manage is Saharan dust.

I believe this is our biggest dust outbreak of the season, and it will really hamper things a bit. So while I believe we should continue watching the MDR, and this wave near Africa in particular, it seems that this will be a bit of an uphill battle, especially over the next week or so. Also of note, this Saharan dust is going to overspread the islands in the Caribbean the next few days, arriving in South Florida by late tomorrow or Thursday and lingering into next week, as dust also works toward the U.S. Gulf Coast and Mexico.

Fantasyland (beyond day 10): Some stirring but no substance

We continue to see things stirring in the extended range, but there are no specific storms to hang our hat on in the modeling, with the exception of the wave mentioned above. That could perhaps be an issue if it develops for the day 10 or later period. But that’s really the only game in town right now, or at least the only one we can coherently point to at this time.

One-sentence summary

Subtropical Storm Don was downgraded to a depression yesterday and remains no threat to land, while ex-Hurricane Calvin in the Pacific is tracking toward Hawaii as a tropical storm with some impacts likely.

Happening now: Calvin hobbles toward Hawaii and Don wandering aimlessly

Of most immediate interest, we turn to the Pacific, where former Hurricane Calvin weakened to a tropical storm on Sunday. Calvin is on a course that will bring it fairly close to the Big Island of Hawaii this week, meaning tropical storm conditions are possible there, assuming it can hold on that long. Even if Calvin does weaken, it is likely to bring rough surf and heavy rainfall.

Looking at Calvin on satellite, this is not a particularly strong storm. Maximum winds are 50 mph and continued weakening is expected through tomorrow before it gets to Hawaii. It does have a fair bit of moisture with it, especially on the north and east side which is why portions of Hawaii may be impacted.

Calvin is currently expected to pass just south of the Big Island, though it remains in the cone. Regardless of the specific track, the impacts should be fairly similar. Rough surf is a given, but also some heavy rain is possible.

Current forecasts through Wednesday afternoon in Hawaii show anywhere from 3 to 7 inches on the eastern half of the Big Island, with lesser totals on the other islands. Expect Flood and Tropical Storm Watches to go up later today.

Meanwhile, on the Atlantic side of the coin, there is Don, which is just an adorable system.

Don is a subtropical depression, and you can see why from the satellite loop above, with general disorganization to its thunderstorms (a lack of bright colors near the swirling center). Speaking of loops, Don intends to do one in the coming days.

Don should almost do a complete circle when all is said and done, before it takes off out to sea. There is some chance that Don may reform into a subtropical storm later this week, but we’ll see.

The medium range (days 6 to 10): Atlantic wave watch

There continues to be some support for a potential Atlantic tropical wave heading into the medium range. We briefly mentioned this on Friday with respect to the wave emerging off Africa then. That has since faltered. I would assume this one will as well but there is some model support for something to perhaps come of this in 6 or 7 days.

But to be sure, there are some beefy looking waves coming off Africa right now. If that remains the case in 3 to 4 weeks, it may become more likely that we see something come of them. For now, I would not expect additional development through day 10 of the forecast but I would not rule it out entirely.

Fantasyland (beyond day 10): A little noisier

The extended reaches of the forecast push us into August now, closer to the ramp up in typical hurricane season activity. The GFS model has at times taken that wave we discussed in the medium range section and brought it toward the U.S. or Caribbean islands as a coherent storm in the day 10+ period. But it remains sort of on its own, so we will ignore it specifically for now. Outside of that, there is nothing in particular to pin down.

We had no storms in August of 2022, but based on what we see happening in the atmosphere to kick off August, we would not expect a repeat of that quiet in 2023. Nothing specific to hone in on yet, but we’ll keep you posted.